RIM can't keep a stranglehold on having decent Exchange integration forever. Many corps already want additional tools to use on the BBs than just exchange integration. You'll have stuff where people want to be able to check inventory for anywhere, hook into the company ordering/ticketing system, whatever. And they're willing to have these apps developed for them (usually in house).

Whenever RIM loses their edge in exchange integration, if corporations ability to create custom apps is still crap, then it'll just be inertia keeping them as the 'not wrong' brand. And that inertia will fade.

As it stands now, I've seen two corporate teams developing BB apps for two companies from a distance. And it sounds painful. I mean, just running the simulators is kinda painful. I swear that the simulator can take longer to boot than the actual handhelds sometimes.