What happened to RIM is that all they were left with was their hardcore, email-addicted, security minded end users and corporations. But that proved to be a small subset of their overall user base. The majority (me) jumped ship when the iPhone came along. Why? Mobile email was critical to us because we were always on the move. The apps that you could get on the iPhone - whether a 2 hour movie for a plane ride or a flight app that let me understand where my plane was before the gal at the counter did, or maps that let me find a Starbucks near the meeting - more than made up for the slightly less (then) optimal email vs a BB. RIM had to move. They just moved poorly because they couldn't adjust.
The RIM situation was even worse than you describe. It was actually very similar to Nextel's earlier fast rise and collapse.
They saw erosion in their enterprise sales, but missed the fact that the superior web browsing experience and eventually applications on the iPhone was driving folks away. They honestly thought that their keyboard was still a key differentiator that folks cared about.
So they stuffed the channel in the low end of the market, and pushed the cheap text messaging of BBM as the core offering. Suddenly sketchy cell phone kiosks are pushing BlackBerries, and they became the new T-Mobile Sidekick. Just like with Nextel, that low end push tainted the brand, as thugs and drug dealers learned quickly that BBM (like DirectConnect) was initially not interceptable.
