I do think there are more complains about the MBP then the MB though.
I would speculate that its due to MacBook Pro users being a more demanding bunch (that's why they went through the trouble to spend more money).
4) Heat. The MBP is fantastic and I've got no concerns about it running too hot but that metal shell does, by design, make it hotter to the touch than a MB. This goes double for situations where you're ot getting proper cooling to the machine (on a lap, in bed etc) where a lot of 'casual' users will actualy be using it.
I just want to point out something about this one: I've done what some people might consider a ludicrous amount of tech support; and my observations are that the "casual" users are actually the ones most likely to put it on their desk, and leave it there at the end of the day, and it's the more advanced users who are toting it around with them everywhere and taking it to bed with them (the geek's teddybear..?).