You assume that RIM doesn't want to keep their customers happy then?

RIM's business is built around steady progression of technology rather than flogging the latest and greatest fashion phones. I'm sure there are plenty of businesses quite happy with their hundreds of old Curves or 8800s that won't replace them with new devices.

However, how many businesses are there that don't want to or can't swap out devices but DO want newer functionality? (Look at HTML email in OS 4.5.)

RIM seem to support old devices pretty well - hence you can get OS 4.5 on an 8700. Long may it continue.