I've done ~15 Windows reinstalls in the last few years, and every single one of them was malware masquerading as anti-virus software. OSX's reputation may make Mac users feel invincible, but Windows users' knowledge of their vulnerability opens them to pretty effective scare tactics.
In fact, it hit my house twice, and I'm not exactly incompetent: Win7, Security Essentials, kept on top of Windows Update, no admin privileges for little brother or mom, updated Firefox, etc. The last time, it turned out we were behind on Java updates - it popped up in the systray 5 or 6 times a day for a few months and the few times my dad tried to allow the update, it failed. I didn't know about that until I was in the room while my brother was using the machine and I saw a dialog that looked an awful lot like Windows reminding you to install AV but not quite right. No way anyone else would have noticed that the background gradient was just a bit off. Did a scan... MSE was showing me 20 different Java exploits and "Anti"virus 2012 wouldn't let me open Firefox again outside of safe mode. Not something my parents would be able to deal with when I'm not there; they would have had to pay somebody. Its replacement will be a Mac; they like OSX better anyway.
I worked for a small-business IT firm for 3 summers and have never seen or heard of OSX malware except from the blogosphere/HN/media. We took our clients' security pretty seriously - corporate domains, enforced Automatic Updates, no idiots with local admin, corporate endpoint antivirus, antivirus in the spam filter, Sonicwalls, Firefox wherever possible, etc. Still, we got virus calls pretty frequently. I would usually babysit the reinstalls at a reduced rate, but when I wasn't interning, businesses were shelling out $150/hour for that. To be fair, most were XP, but there were a few virus calls for Win7.
I don't have statistics, but if you're going to claim OSX has fallen as far as Windows in terms of infection rate, I think the burden is on you to show some data. Again, just as many family friends running OSX as Windows; I've had Macs die (my MBP's motherboard gave out right after 4 years), I've had Macs run out of disk space, I've had the PowerPC/Intel switch lose my family a lot of money because perfectly good ~2006 machines can't run a modern OS or Flash/Firefox/iTunes, but I've never seen malware for OSX.