I don't get why Windows doesn't offer an anti-virus standard...

Because then MS would be using their dominance in the OS market to shoehorn their product onto users, which would in turn lead to more anti trust cases.

I use BitDefender. Works like a charm.

 Because its an inferior OS developed intentionally with holes so you can pawn dozens of updates and support software for it on the poor sods like us who use it, made by a company so influental and controlling they can basically release shit in a jar and charge you for it thrice a year.

Yes, they have some of the most talented (and well paid) programmers in the world make an OS with tons of holes so they can pay those same people even more to fix those holes.

As a side note, it's been roughly 4-5 years since I last saw a computer virus on one of my machines and that was entirely due to McAfee being a poor security solution. 

like alot of people here I also use AVG antivirus free edition ( http://free.grisoft.com/ ) , spybotsearch&destroy ( http://www.safer-networking.org/en/index.html ), and ccleaner ( http://www.ccleaner.com/ ) a great program for clearing cookies, temporary data, and other stuff. All are free to download and use haven't had any problems been using them for 2-3years now.