The best summaries I can find of the Apple/Adobe situation are Jean-Louis Gassée, Steve Jobs via Greg Slapek, and of course John Gruber - though Joe Berkovitz gets an honorable mention for raising the prospect of "metaphysical outrage". In summary: Adobe and other vendors of cross-platform tools threaten Apple by providing lowest-common-denomination abstraction layers on top of iPhone and other platforms, degrading Apple's ability to differentiate their products. As John Gruber puts it, "I’m not saying you have to like this. I’m not arguing that it’s anything other than ruthless competitiveness. I’m not arguing (up to this point) that it benefits anyone other than Apple itself. I’m just arguing that it makes sense from Apple’s perspective — and it was Apple’s decision to make".
What will this mean for the other tool vendors out there, the plethora of port-to-iPhone tools? The web-based ones like PhoneGap seem to stand the best chance of navigating through the new T&Cs, I wouldn't want to be in the shoes of the others. If anything, this all leaves the web strengthened as "the one way to go cross-platform on mobile", a direction it's been heading in for some time, thanks to good HTML5 support on iPhone and Android, and Canvas/video support.
If you need to go native, the Apple Way is now to build apps which take full advantage of the platform they're running on. That doesn't sound like a bad thing for the apps, their users, or to those creating them; and there are increasingly credible alternatives to the unpleasantly controlled Apple ecosystem if you find that unconscionable.
So that's Apple. Oh, and we should probably shed a tear for all those "social gaming platform" companies whilst we're at it; quite a few of them look like they've become commoditised. Is it me or does the way Big Steve said Apple "won't necessarily supplant" these guys sound a bit... chilly? And I wonder what Apple will do with the social networks they start building off the back of gaming...
The other interesting one was Twitter, who've purchased Atebits, the makers of Tweetie, to help them "provide the best possible Twitter experience on all of the major mobile platforms". Again, not good news for any of the other vendors of Twitter clients for mobile devices, whose best outcome now is that they can flog themselves or their products to Twitter before their out-distributed; I should imagine that as Twitter goes more mainstream, an "official" client will steal audience from any unofficial ones.
Some of the unofficial clients feel like labours-of-love, but some of them are businesses. Let's not consider how advisable it is to build a business on top of a platform provide you're completely locked into, who's not themselves worked out how to make money...
I think there's a particular problem with web businesses opening up APIs right now. The issue is that large chunks of audience are starting to come from mobile; that these APIs let third parties service these audiences; and that at some point most businesses don't want a significant percentage of their audience being serviced by a third party they have no control over - particularly when this "servicing" involves the bits which end-users engage with and build loyalty to, the user experience.
This is, of course, a subset of what you might do with an API (combining data from multiple sources is a different case) - but it's a big subset, particularly given the rise of mobile at the moment. I think we'll see a lot more of this sort of thing; what will Yahoo do should the lovely unofficial Upcoming app for iPhone prove popular, say?