[Angrist]

Sony tried to give gamers hardware they didn't need yet. The Cell processor is nice, but the 360 gives graphics that are just as good.
Bluray, sure why not, but it sure does make it expensive. People just aren't ready to pay for it.

Not enough good game exclusives.

One of the things that might have hurt them the most was the bad publicity they got. First the banana controller, then the change of controller. Then the added motion controls which was clearly another "Me too!" move. Then the terrible but epic E3 presentation. Giant Enemy Crab and Riiiiidge Racerrr will go into history as some of the greatest quotes.
Suddenly everybody was laughing at Sony. Even I felt more for the 360 than for the PS3, while it was the other way round a year earlier.

And the expensive hardware may all for the long term, but it just doesn't seem to work yet.