In an article about the relationship between Apple and Adobe, Hardmac speculates that Apple may have alternatives to Adobe's cash cows in development. Given how openly Steve Jobs has been trashing Adobe, that speculation seems well-founded.
Consider that the situation in which the Mac was no longer the preeminent creative platform would be anathema to Apple, something they simply could not allow to happen, no matter what.
Consider also that Apple introduced Core Image to Mac OS X as a part of 10.4 Tiger, nearly five years ago, since then integrating it into their own applications, including Aperture, Preview, and iPhoto, and encouraging others to make use of it, Adobe included. Two third-party applications in particular, Pixelmator and Acorn, have taken this offer and run with it. By taking advantage of the head start Apple provided in Core Image, they've quickly established themselves as the main contenders among Mac-only image editors.
This is typical of how Apple works in many cases, laying the groundwork in the form of system libraries, available for use by any developer, and folding them into their existing software before deciding to take the next step and use those libraries to build their own pro-level applications. Exceptions typically relate to new, secret hardware projects.
Considering Adobe's reluctance to invest in Mac OS X has been apparent for years, it's very likely that Apple has been working on their own pro-level image editor since before Tiger came out, and that by this time it's well polished and ready for market, likely to be reviewed as better than Photoshop® by the preponderance of reviewers, in the event it is released.
But I doubt that Apple would fire shots across Adobe's bow unless they had more than a Photoshop® replacement ready, or nearly so. Chances are good that they are at least a long way along in developing replacements for most or all of the major components of Creative Suite®. I wouldn't expect a one-to-one correspondence between Adobe applications and their Apple equivalents, but Apple very likely has nearly all of the functionality of CS covered, in one way or another (in particular substituting HTML5 for Flash). At this point the choice whether to go to market must be reduced to about the same level as throwing a switch, and the only thing providing Adobe with a bit of reprieve is that Apple doesn't want to distract attention from their new iPad, due out in less than two months.