BlackBerry's biggest selling point is that it's optimized for business (especially allowing secure connections to a corporate network). From a tech point of view for games, it's not clear that the platform gives much of an advantage over iPhone or Android.
A few selling points are the following:
* Smartphones are a growing market, and BlackBerry is still holding its own (in market share) against competitors (Android and iPhone). So there are (and will be) a lot of devices out there. (And you can subversively allow people a distraction during boring meetings.

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* BlackBerry App World gives you a more favorable percentage of your sales revenues than the iPhone app store (and places fewer restrictions on what your app can do).
* Since BlackBerry supports J2ME (and even MIDP), it's easier to write a game that will run on both BlackBerry smartphones and on mobile phones (where J2ME is the industry standard).