It's still a much better platform from a virus point of view than Windows by a million miles. The chances of you getting infected on Windows remain substantially higher and will remain so for the foreseeable future.
Again, because of the numbers involved. Same as with Android phones v iPhone (or Windows phone, or Bada, or what Symbian exists nowadays). Quantity of users is the biggest draw, as well as the open source OS.
Simple fact of the matter is that you do not need antivirus on a mac if you follow basic maintenance steps and common sense when on the internet. I have checked all my macs for the presence of that virus, on none of which I run an AV, and have not found it.
Simple fact is that at least 500,000 mac users don't have that common sense approach and, honestly, would be the same as windows users who think that the AV that came supplied with their PC is all they need and have never updated something that was only good for 3 months. As the number of users grow, along with the "users" that should have a keyboard lock fitted and only bought the Apple as it's "fashionable", that proportion will grow and lead to something even more attractive to those with bad intentions.
This ain't the first virus on a Mac OS, and it certainly won't be the last. Your "Windows Experience" is on it's way.