Just to add to this debate as I'm also a PC player - I have spent a lot of time perfecting routes and so on for the PC - I don't think there is any difference between the two in terms of physics or frame rate - I mean Orion, we found that turning the frame limiter on for some races made no difference to the overall time - World War Aces for example.
I really think they could be on a level playing field - I mean perhaps I could post a video of me doing one or two of the races to see if any of the PS2 guys do anything drastically different? As so many of the times are close or the same, I think it's just a matter of some races having been tried more on PC than on PS2 - I mean we have some serious competitors between me, you and GTA_Phreak, constantly pushing each other, whereas I notice here that many times aren't quite so closely contested...
On the motorbike times you have pointed out, I play with a keyboard and am constantly tapping "W" in races to lean forward, but it does knacke rmy hand after a while. I thought 1:55 was the best I could do on Desert Tricks, but trying it over and over and perfecting my line proved me wrong - same was true for Dam Rider, Barnstroming and Dirtbike Danger. PC controls (at least with the keyboard) don't allow you to stay ducked at all times, no matter how much you press "W" - you wouldn't want to on some races anyway.
I think later on this evening, I will post a video of me doing Dam Rider and show you how much I can duck to see if it's really any different. I'm not saying I'll do a 1:46, but I can consitently get under 1:50, even wit the FPS being low on recording.