They still provide a level of central control unmatched by anyone else. By that I mean central control by your nazi control-freaks rather than someone else's.
Name another device where your admins can determine exactly what it can be used for, exactly what is and is not allowed on it and the use and type of passwords in such a way that there's abso-ruddy-lutley nothing the end user can do about it, no matter how savvy in the ways of the hacking tools he may be, without wiping the thing irrevocably. There are plenty of ways of removing BES policy from a BB, but I've yet to see one that preserves its content when doing so.
You can also bet that, should a technique for doing so become readily available, RIM will have an update out locking that door, welding the locked door shut and burying the whole arrangement in reinforced concrete before you can say "Jack Robinson".
That's why they still rule the corporate roost and I've yet to see anything on the horizon that might change this. It's also why, despite heavy pressure from TPTB, I haven't got one.......