I disagree, everyone I know who are tech geeks use a mac and can do just as much or even more than with pcs.
Its true that PC users are mostly gamers that like the best of the best hardwares and download lots of different drivers to fine tune their GPU or overclock or whatnot.
Anyway I used to be one of those guys with PC's but when it comes to downloading music, movies, streaming, rendering, whatever you name it, I can do it on a mac just as easily (and yes you have to d/l software outside of right out of the box of what OSX offers to do much more).
Thats how great OSX is, if your an advanced user (tech geek) you can do so much more while the UI is much nicer/simple and its even greater when you have no knowledge and are illiterate in anything that comes to a computer. Thats what makes a great OS in my book.
My mother uses a macbook I handed down to her and since day 1 after explaining a total of 15 minutes on how to get online and check email, the past 3 years she never once called me to help her with anything nor messed up the OS where she accidentally deleted something or moved something she wasnt supposed to. (And its a different story for my father with a dell, where I had to reinstall windows a few times in the past 6 months because he accidentally moved something or erased something he wasnt supposed to).
My point is that when I was a PC user, I always thought macs were crappy because: 1) You couldnt game, 2) You couldnt download music, movies *cant really discuss this stuff here I guess* 3) Too expensive and none of these are true nowadays.
But these days Macs are great priced for what you get for the features/design, etc.. and I can do anything I want on a mac as I want to do on a Pc.
First of all, sounds like you hang around with a lot of Geeky mates who use a Mac, fair enough, though if you want a better understanding of your average mac user, spend sometime down the apple store near the Genius bar and listen to some of the issues they deal with.... you might change your mind. Heck, just read through these forums. If we are to stereotype, PC users are geeky, Mac users are creative.
In relation to "use a mac and can do just as much or even more than with pcs" this is just plain incorrect, you need both to get the best of both worlds..... since you brought up gaming lets use that as an example, gaming on a mac frankly substandard due to huge lack of games and inferior GPU driver support, ATI and Nvidia release drivers on a monthly basis for PCs that dramatically improve performance, the Apple ones never get updated, if anything they underclock the hardware so its more stable, and run GPUs way behind a PC (look at the Mac Pro...its a generation behind). But people who only use a mac will throw up their trump card..."But we have boot camp, so we get best of both worlds!" Well reality flash......once you go boot camp you are running a PC... beyond the design, the guts of a Mac are now the same as a PC. There is a very good reason that apple went down the Bootcamp path, they realized that if they wanted people to switch they would still have to offer them PC support.
PC users are mostly gamers, are you serious???? Who do you hang out with? sounds like your at university.....the gaming market is a very small share of all PC sales. If you are suggesting of the 90%(there abouts) market share that Microsoft has, they are mostly gamers... come on!. Google PS3, Wii and 360, PC gaming is a dieing art for the hardcore (but small segment), frankly consoles are killing it, and more game developers are developing games for consoles then PCs, this is a know fact. Trust me your average PC user would have no idea what overclocking is, nor would they even know that they could update their GPU drivers. Mac users are not Geeks and PC users are not gamers.
"downloading music, movies, streaming, rendering" hmmm Both a PC and a Mac will do these just fine. I think you are hinting at torrents, well PC has alot better clients for that. BTW, talking about torrents is not illegal, neither are torrents, its just p2p file sharing, piracy is only one element of it. Just like the internet is not actually about just porn and piracy...)
Also next time your in your local computer store have a look at the hardware, there is a fair amount of very nice gear that is not supported on a Mac. Same goes for alot of MP3 players. Thing is a PC user can walk into one of these stores and everything but an apple product will work on the PCs, Mac users are not so lucky, the same goes for Software (alot is not supported on a mac). Look at the logitech line, alot of PC only goodies there.
As for you Mum and dad example, If you dad did the exact same things as your mum the the PC be fine (visited the same sites etc) To me it sounds like your dad does alot more then your mum on his PC (installing software, visiting questionable sites

etc.
Macs are so much more safer then PC, and alot of it comes down to how easy it is to install software on a PC, download and click on the exe....bam! your on your way to messing up your OS cause you just installed some random program. On a Mac, not so simple, frankly most users have no idea what a DMG is, or how the heck you install a program. I just went through installing AC3 support on my Mac, On a PC its running an exe file, on the mac you have to put the codec manually into a library....you average user would have no idea how to do this, expecially when they are used to running exes.
As for
1) You couldnt game - In OS X, very limited game support, slow drivers, GPUs a generation behind.
2) You couldnt download music, movies - Any OS can do this, heck u phone can
3) Too expensive and none of these are true nowadays. - They are expansive for comparable hardware
To be really honest, and since i use both on a daily basis, its the PC i could not live without. The PC can do everything a mac can, but some things not as well (so instead of hitting my head on a brick wall i just get it done on a mac), but a Mac cannot do all the things that a PC can. There is a very good reason Macs run Parallels or similar vmware. Without it, there are just things you could not get done. For most people getting a mac is a lifestyle choice, not because they need one to make a living off.
I love my MBA to death and it is my favorite computer, I also have quad SLi PC gaming beast and run linux on another laptop. Depending on my needs I will use the one that suits situation. To say that one is as good or better then the other for everything is being very close minded. And no, I cannot game on my MBP, especially when i compare the experience to the PC, its like asking a mac user to be seen with a dell when they are used to showing off with a mac, not going to happen.
I'd recommend for anyone to download and try the Windows 7 beta, especially the ones that have been traumatized by vista, if you try it at least you have experienced it and you will have a stronger argument in the OSX v windows saga.