Pro Users
Regarding Apple and future applications being a photoshop killer, I see this as fairly unlikely.
Relationships between Apple and Adobe haven't been like they used to be lately, but there's no real rancor there either.
Adobe know that Apple users are a major market for their software, probably more so than just about any other software company, especially Photoshop and Illustrator.
Apple similarly know that Adobe Apps, again esp. Photoshop and Illustrator, are a key app in their lineup. They don't use it in their benchmarks for fun. If they lose Adobe's support, they lose a massive slice of an already tight market.
Designers by nature are quite fanatical, I've noticed. The pairing of Photoshop on Apple is an established standard. Anything that shifts that balance will NOT be to the wishes of these designers.
Apple's iPhotoshop (hypothetical and stupid software title) would be met with disinterest by even the most hardened Apple zealot who relies on a complex and polished package like Photoshop.
And such a release WOULD anger Adobe. The next version of Photoshop would be XP (or Longhorn or whatever) only, ala Premier.
Apple would then be forcing its users to abandon its own platform, or completely re-learn a major design tool. This is NOT a decision Apple want it's users having to make. This is not a decision Apple will allow to become even a question. Apple will stop at iPhoto. A respectable piece of software, though not as innovative as Apple want to suggest. (ACDSee has been doing most of it for years. On Mac and PC.)
At very most some Apple program such as iPhoto might take on some "Photoshop Elements"... er... elements. Basic digital editing for the consumer, digital camera crowd.
But they don't want to upset the balance in the professional Photoshop crowd.
Just my two cents. I'm usually wrong about most things.
Later!
Matt