Within a couple of years it is likely that many of the user interface features that currently distinguish the iphone will become a commodity. The first phones with similar features are just now coming out. It is possible that the iphone will then follow the path of the apple II and macintosh, which were just as innovative but failed to give apple the success of competitors who eventually produced similar products on an open platform. Will andriod be the open platform that steals success from the iphone as windows and dos did from the macintosh and apple II?
Nope! And it's because Apple provides a better user experience. And Google can't fight back entirely, because they don't control the hardware, and - furthermore - because they need to adapt their software so that it can support whatever hardware wants to use it.
That's not to say that I think Android will be bad - just that the iPhone will be better. And as a result, despite programmers' gripes, it will have more potential and - much more importantly - far more users. People won't switch operating systems just because it's more open than something else, only if it provides something more. It's not like the Apple II, which lost to Microsoft's products because Microsoft appealed to a different market. That different market is already led by Blackberry and Windows Mobile, and Apple's aware of that.
It's possible that Android becomes wide-spread, if all the cell phone operators decide to pick it up. But that's a lower market than the one Apple appeals to. Their market, the "multiphone" for lack of a better word, is one that they created and they are leading. And I'd guess their goal is to make that market the dominant cell phone market. Whether or not it succeeds has nothing to do with Android. It has to do with whether or not the market shifts with Apple.
The problem is that beyond events like WWDC, apple really has no place to discuss anything NDA'd - not just the iPhone SDK, but things like developer seeds as well.
I'm betting the iPhone SDK NDA will be lifted someday, just right now it makes zero sense.