MikeB on 04 April 2009
A cross platform PC centric gaming engine which had issues initially was Emergent's Gamebryo Element engine (Oblivion and Fallout games use this, the quoted comment below is from a Gamasutra interview with the technical director)
"faced with the problem of converting our mostly single-threaded engine"
So on the PC they probably only took advantage of dual core processors. One core running mostly the host OS and another running mostly the game. Owning a quad core PC during the pre-PS3 era would not yield gains for mostly single-threaded game engines.
To take good advantage of modern PCs and the PS3, this gaming engines would have needed an overhaul (and probably they have significantly modernized this technology since).
