As a programmer, I can tell you first hand that making an app for iPhone and Blackberry are totally different animals. Whereas there is only 1 iPhone, there are several Blackberries, so making an app that works on all of them would definitely be a heck of a lot more work, and even then would be a far less user friendly experience than a similar app for an iPhone.
Its the same as programming for MacIntosh vs Windows. The MacIntosh has a few set hardware skews, whereas there are literally an infinite number of hardware permutations for Windows boxes.