The BlackBerry market is made up of corporate users who write emails that go on for miles. What makes the device unique is they physical keyboard, which makes it easy to write those monster emails. And in my experience of hanging out with Blackberry users that's really what they use the device for — the ability to make a phone call seems secondary (and the ability to look at the web isn't even there).
While the other brands appeal to the consumer market, corporations still love their BlackBerry in the way they love Windows. If RIM was smart they'd get acquired by Microsoft, Oracle, Dell or IBM — someone who is a top tier player in the corporate space.