The killer app on the iPhone is the appstore.
But, the thing that makes the appstore so necessary is that the iPhone needs it. The iPhone comes so bare-boned that it would be much less functional without the appstore. Most (but certainly not all) of the iPhone's deficiencies are corrected by the appstore.
However, in contrast to the iPhone, the Pre already has these functions pre-installed. Then, it takes another step and incorporates all the functions that Apple refuses to allow on the iPhone; c/p, background apps, mms, video, gps, etc.
Think about the number of apps you actually use extensively (on an everday basis). Either these apps/functions already will come on the Pre or it really will not be much of a problem to go to the developers website and download the apps directly. In this regard, and also due to that fact that the appstore is 99% garbage, the Pre is going to make the idea of an appstore irrevelant.
Also, why is this thread in the iPhone forums? As an iPhone owner, I fail to see how this is relevant to me.
No offense, really, but if your going to write stuff that that, you should also ask yourself why you not only clicked on the thread (given its title), but also took time to leave a fairly lengthy response. Just saying...