You really don't know what you are talking about, do you? Do you even know why there is a need (ever) for CPU affinity? Sorry for being argumentative, but multicore systems happen to be my bread and butter...
I am willing to accept that the Operating system can handle these issues, but not that the processors can (the current lot can't at any rate).
Certainly, perhaps with the newer drivers you can get around the bugs that sometimes occur on running some single threaded programs on multicore computers (Thief 3 comes to mind..), but there are many other issues involved. I do think however, that setting an affinity is at least conceptually a bad idea, but at least with Linux, it may some times be required (I haven't performed the same tests on Windows)