Two reasons:

1. It's Apple, everything is supposed to just work. As a web developer, I not a huge Flash fan. But if I'm on my iPhone or iPad and I get the "missing plugin" brick, I'm pissed: I'm missing out on content. Steve Jobs wasn't telling the whole truth when he said it was the "real internet".

and 2. Flash was introduced almost 15 years ago. The fact that Apple is today announcing a magical device with a touchscreen and a blazing fast mobile processor, but one that cannot run a plugin that my grey Gateway 2000 Pentium I desktop had no trouble with just seems backwards. I don't know if it's an Apple problem or an Adobe problem, but it's what you get when you mix two companies with closed software standards.