That's not really correct. Adobe's announced that they're working on optimizing Flash for ARM and low-powered devices. That's basically an admission that Apple et. al. were right, and that Flash is a bloated, buggy piece of crap on anything that's not Win32/x86.
Could Apple put Flash on the iPhone at this very moment? Yup. But you wouldn't like it. You really, really wouldn't like it. I've used Flash on three architectures (PPC, x86, and handheld ARM), and I can say without a doubt that its performance on ARM-based handhelds is the worst of the bunch: it's absolutely horrid.
Personally, I don't use Flash. At all. If a site requires it, I find a new site. It's a proprietary extension to the web, and it's a very inefficient, non-portable way of doing stuff that can be done just as easily (if not more so) with Javascript and CSS.