A lot of it has to do with the presentation...
Microsoft is still learning this whole "console thing" and it shows in their presentations at big gaming expos..
Although Sony has a history of Powerpoint Madness (TM), they seem to have a better understanding of how to communicate with their fans....Sony may not listen to their developers as well as Microsoft, but they really know how to give their core fans what they want....moreover, they seem to learn from thier mistakes somewhat (as far as showing their fans the goods)....
A PlayStation presentation is usually VERY slick and professional....moreover, they are consistantly so.....sometimes Nintendo will have a good game showing (E3 2K4) and sometimes it seems they are going through the motions (E3 2K5)....plus, Nintendo is not at all forthcoming with the information their hardcore fans desire because Nintendo doesn't want others to "steal their ideas" (I don't know if Nintendo actually buys this line....but I hope they dont, because MS/Sony could probably care less what Nintendo does because they are focused on each other)...
MS is getting better, but the growing pains are obvious....
I am personally stoked by Ridge 6, Winning Eleven is big news and PGR3 looks great, but the stuff that usually comes out of Sonys presentation are usually pretty jaw dropping...
Thats my take on this....