I'm with you for the drivers, I guess most of them could do what e.g. Massa does if they had the chance to sit in a Ferrari - and he's not that much slower than MS.
And while I see that you do not want to suggest that Ferraris and Super-Aguri s are "equal(ish)" cars, I don't think the reason a Ferrari (in most cases) can't overtake a Renault (and the other way round) is that both cars are equally fast. Because in fact, you often see that even if the following car is 1 or 1.5 seconds faster it won't have the slightest chance to overtake, unless the driver in front gently lets him pass or makes an error.
I actually blame the FIA for reducing mechanical grip (for example banning slicks) instead of downforce (dunno.. reduce wing size, ban all those mini wings and displacements, whatever) to slow the cars down. (Reducing engine power was probably a good idea though, just didn't work out at all lol).
I mean, the main reason overtaking is so hard in F1 is imho that you lose so much time without "fresh air" (because the cars rely so much on a proper air flow to have enough grip, see above).
Having said this, I don't want to claim that GP2 only has more takeovers, because the cars rely less on aerodynamics (you have to admit, that they look much "simpler", though). Surely different driver skills have an impact there, too..
Anyway, guess I'm slightly off-topic here..