It's not having actually gotten a virus that concerns me when I run Windows, but the fact that they're out there. How safe do you feel shopping, banking, etc. with a Windows machine? They get new keyloggers, etc. all the time. If your virus checker hasn't added it, you could be the one that gets screwed. Compare that to OSX that has never had more than trojans and worms and very few of those. You can talk about risky online behavior, etc., but I'm talking about feeling secure. That's harder to put a price on.
My old gaming computer is still running XP so I'm talking about updating its virus checker yesterday. Is that recent enough? Yes, Windows7/8 is nicer in terms of an operating system. That doesn't automatically mean it's more secure than the final Windows security update. They've been updating them all along side each other. I'm not talking about how well Windows8 runs (I don't like Metro).
I'm not saying I haven't used Windows7 or 8. I have at work, etc. I simply don't feel any need to get it at home since most new games STILL work in XP and that machine is getting out of date anyway. I don't game as much as I used to and have dozens to play in OSX now first anyway. Family members have Windows7 on their machines (I updated my mother's computer for her all the time running Windows7 before I finally bought her a Macbook that she uses 50x more often now). They STILL require virus checkers. That has not changed.
What does that have to do with the current state of malware? Are you claiming Windows7 and 8 are more secure than the final security patches for XP? In what way? Maybe you mean that they ask you if you are sure you want to run something (Vista was REALLY good at doing that over and over until you were sick of it)?

It's STILL Windows, not UNIX and has 10,000x the Malware out there of OSX and that's being conservative. Ever look at a Virus checker database? There are tens, if not hundreds of thousands of viruses for Windows. There are ZERO for OSX (and I mean a virus, not trojans/worms).