NFI, I take it that those prices are not in US Dollars, right? Because I'd love to be able to get an 8800GTS for under $200.
As usual, Paparazi has it dead on. Some companies do extra engineering to get their cards to the higher clock speed. Others don't. Many people have reported success buying slower clocked cards and then overclocking them on their own, though success is not guaranteed.
Realistically, you probably wouldn't be able to tell the difference without running benchmarks. The OC and OC2 cards would be faster than stock, but your eyes probably would see them as the same.