I don't think they've shot themselves in the foot at all. With QNX you've got a fully Posix compliant OS. This makes porting *nix based apps, of which most phone OSs are based today in one shape or form, very simple. Secondly consider the other common frameworks RIM have included, Adobe AIR, ActionScript, Webworks and standard C++. These are completely portable between platforms. Then consider things such as the Unity 3D game engine (
here running Samurai Vengance 2 on PlayBook,took minutes to port apparently from iPad). Then consider that the PlayBook can run Android apps with, in some cases, NO modification at all.
Combine this with an App Store that has a higher revenue in total than Android Market and the highest $ per App revenue value
of any App Store means that a developer would be foolish not to at least try to take a slice of the pie, especially when the door to entry is no longer a restrictive Java only environment like BB OS. Then they are also in front for when QNX based phones are launched, as they have experience and presence in the market.
In reality, rather than shoot themselves in the foot, they've shot themselves back into the game.