Steve Jobs likens not supporting Flash to getting rid of the 3.5 floppy disk or HyperCard on the Mac. Adobe never showed them Flash running Fast. Apple didn't think they'd use it. They have limited resources and choose to back horses they think are on the rise and not on their way to the graveyard. Apple didn't use Flash on the iPhone but after they didn't use it on the iPad Adobe rose a stink. Apple didn't talk to press but enough was enough, and so Steve Jobs wrote his open letter, "thoughts on Flash".
(Note: it was probably the ban on cross-compilers, not the lack of Flash on iPad that got Adobe steamed considering how much they'd invested in Flash CS5 packager for iPhone.)
Video after the break!