Flash Player engineering manager Paul Betlem, as relayed by John Mack:
First and foremost, Flash Player 10.1 is a full-fledged Cocoa app (though legacy Carbon support remains for some browsers that require it). We now leverage Cocoa events, use Cocoa UI for our dialogs, leverage Core Audio for sound, Core Graphics for printing support, and use Core Foundation for bundle-style text.
I'm happy for you, Adobe, and imma let you finish. But Creative Suite 5 was also written in Cocoa, and even though it uses the same Apple frameworks I'd hardly call that a successful Mac-native UI.
Still, Flash Player has been one of the least Mac-like apps in common use, so any progress is good progress.
The boss speaks:
Our motivation is simple – we want to provide the most advanced and innovative platform to our developers, and we want them to stand directly on the shoulders of this platform and create the best apps the world has ever seen. We want to continually enhance the platform so developers can create even more amazing, powerful, fun and useful applications. Everyone wins – we sell more devices because we have the best apps, developers reach a wider and wider audience and customer base, and users are continually delighted by the best and broadest selection of apps on any platform.
This works just as well as an explanation of Apple's overall strategy—their products are platforms for other people's content (e.g. music, movies, apps, books), and if you make the best platforms you'll attract the best content, which'll attract customers and make everyone money.
So, they don't have any known crashing bugs, and until now haven't seen much need to actually write a Mac-optimized version of Flash Player. Except now they're rewriting Flash's graphics engine, going from a direct port of the Windows version to new Mac-optimized code that makes use of Apple's Core Animation framework.
While a lot of the attention has focused so far on iPhone/iPad, this is the part really worth watching: Adobe knows Flash is a performance hog on Macs, and Macs are now finally a big enough (consumer) deal for them to address it.
Bonus nerdery: Flash engineer Tinic Uro discusses the technical details about why Core Animation and Flash should be like peas in a pod.