Many websites such as PCgameshardware, LegionHardware, Techspot, Gamegpu.ru, Xbitlabs reported that dual-core CPUs were limiting GPUs in the last 2+ years. Not everyone agreed with this assessment. I don't think it's accurate to say that no one else could replicate slower performance with dual core CPUs in Resident Evil 5, GTAIV, Supreme Commander 2, Far Cry 2, Arma 2/3, BF:BC2, etc.
toyota was one of the few guys on our forum out of 100s of users who would bring up specific games such as BF:BC2 where his dual core E8500/E8600 (forget which one) was often not giving him optimal performance. He did this so that other enthusiasts wouldn't throw hundreds of dollars on GTX570/580/6970 hardware and then be disappointed since they wouldn't be getting optimal performance due to their slower CPUs.
toyota also provided feedback to users who had similar GPUs as him (i.e., 4870/4890/GTX260/275, etc.) that upgrading to a much faster GPU (GTX470 in his case) wouldn't solve their problems in many modern games due to CPU limitations. He did this despite many users who claimed that his performance was somehow unusual, somehow related to his "poor setup: drivers, bios, etc. etc.". At least 4-5 professional review websites also showed similar findings to toyota's that C2D generation (or Athlon II CPUs for that matter), even when overclocked, was simply bottlenecking many modern GPUs.
Even now, with more and more games coming out that use more than 2 threads, we still have threads where people ignore CPU limitations and purchase $250-300 GPUs to pair with their stock E6800/E8400/Q6600/Q9550 CPUs.