I think it is because the retailer is temporarily cutting the price to the one with the heatsink to attract customers (NewEgg is offering the same product for $299.99) while they did not cut the price to the OEM. Otherwise, the OEM would be cheaper. I find it odd, however, that they did not cut the price to the OEM too because that will not make people choose the OEM version.
Thanks bro, I was wondering the same thing. I guess the crucial detail is that the CPU's are identical. The listing is from the Canadian branch of TigerDirect. I try to avoid shopping there due to an unpleasant experience I had a couple of years ago. However, I do use their website for pricing for retailers that price match.