i don't think it is any coincidence that routinely the best overclocker motherboards are Abit with no sound, no LAN. without modifications, the high FSBs and OCs are achieved with KT7A, KR7A, and KX7-333. some of the worst OCers are always Soyos and ECS, the ones with the most built-in stuff (all ECS doesn't usually have a lot of options). granted, Abit have the best MOSFETs with 3-phase power regulators and the best BIOS.
agreed, i have no evidence that it is integrated devices screwing things up. Abit RAID boards do very well too in fact, but it may just be Abit's superior device and manufactoring that makes them better.