At least Microsoft's ads show more 'truth' than Apple's. They didn't have to do this but they did...unlike Apple's ads that make PCs look like they are crashing or getting a virus/spyware from left, right, centre, above and below every minute of the day...
So here is a true tale from my summer vacation...
While visiting my father, the entire family (kids age 6 to 17 and adults) sat down for dinner. My step mom had been checking her email on the computer which is located on a desk in the dinning area. She had closed out of the web browser and the computer was sleeping when about 5 minutes in to dinner the computer woke up, the browser (IE - not their default browser) launched full screen. We really didn't notice until nude pictures started to appear on a web page which automatically launched with hard core sex scenes right in front of my 6 and 8 year old daughters. We had to shut the computer off as the sites just kept popping up.
Their setup was a firewalled version of XP SP3, firewalled router, up-to-date versions of XP/anti-virus software/anti-malware software.
It took me 6 hours to figure out what the problem was, find the fix and repair the machine. The problem - it was malware which my step-mom clicked on so yes, her fault but it was caused by a legitimate email sent by her son from a bad website that they always use to create custom ecards. The malware was so bad and even had self healing properties to it and very sneaky in disabling just portions of the anti-virus/malware software. I should mention my step-mom isn't computer stupid and is aware sites can install bad software as well as try to trick you. I would consider her to be an average computer user.
I couldn't believe how bad this was and how easy it was for them to get infected. So being the mac guy I am, I gave it a test on my mac. Knowing the site and email was bad, I visited it on my mac in Safari, Firefox and Camino. I clicked on every link my step-mom told me she would use. After almost a week - no malware or virus on my mac - shocker there.
So, prior to this experience I might have granted you Apple was over exaggerating the CURRENT shape which Windows is in regarding virus/malware. Not from my experience.
No matter how you cut the experience above - user error, bad anti-virus/malware software, poor computing practices - the bottom line is MY MAC DID NOT GET INFECTED. I have NO anti-virus software installed, NO anti-malware software installed and I disabled my firewall during this time period. This is a BIG deal to the average user. My step-mom's computer is only a year old and was slower than molasses due to the malware. The cost of the computer also had an on-going annual cost which is hidden to most Windows users and that is the annual anti-virus/malware software update fees.
BTW - had to send instructions on how to fix the problem to my step-mom's son, daughter, and cousin as they were all infected too. I didn't have to send it to one of her brothers though - he uses a MAC!