Is it possible that the cause and effect are reversed? I thought RIM was established in Waterloo because Waterloo was already by that time a Silicon-Valley-like (or at least Pittsburgh-like) tech hub.
That could definitely be partly the case! After reconsidering it's definitely not fair to attribute the regions success entirely to RIM. It also probably has a lot to do with the University of Waterloo, which (being much more recently founded than other Canadian universities) has always had more forward thinking STEM programs and faculty, and also has much better IP protection for students than other schools in the area.