I just browsed Safari and listened to iTunes, solely, with no other app running, for the last 4 hours, and now I have 4.2GB free out of 8GB. Safari has only 4 tabs.
So I'm starting to think that we'll see a "is 8GB enough for the average user" next year, and I'll bet on myself saying something along the line of "get 16GB because it's less than $100 and it stops the beach ball".
Seriously, though, I do think that computers have grown to the point where we simply need more RAM... and more storage.
The nature of *nix is that it will make use of all the RAM available to it, even if it doesn't need it. If you took out 4GB, I doubt you would see any change (unless of course you're doing anything particularly demanding in photoshop, but then I would argue any photoshop user cannot be classified as a bog standard average user).
I had a friend who ran a little linux server. He knew how to chuck bits and pieces together and run a few Linux commands to get a basic home built Linux web server running, but not much else. Anyway, he had phpsysinfo running which kept telling him the machine was using 99% of its memory. He chucked gigs and gigs into that machine before I told him what was happening.
As above, I'm not even running Photoshop, and I'm already feeling the constraint of less than 8GB.
If *nix makes use of all of the RAM available for it, then the truth is still that more RAM is better, as it can make use of more in that case.
If average consumers are to be the guinea pig, I'd bet that many of them wouldn't even know how to quit an app completely. In which case, more apps will just start eating up RAM more, unless OSX has a mechanism to force an app into suspension like iOS when memory runs low, which I know for sure it doesn't. If OSX runs out of RAM, it simply makes use of the swap files, and that's something that I can easily trigger with Photoshop running.