What happens, in my opinion, is companies become complacent, Look at Motorola and now Nokia. They hate to change a winning formula and it was evolution after evolution and they're market share eroded. Motorola is now probably the most hyped phone since the original iphone with the two pending Android releases.
I think RIM could have done more with OS5 and the latest phones, for example, the 9700 really should have had a touch screen. The trackball is a dated interface and the trackpad, from the videos I've seen, isn't really better. Maybe a pressure sensitive device like the ThinkPad trackpoint would have been better so you can quickly scroll web pages as that's what consumers do as opposed to enterprise users getting mainly email on the device.
More than the other companies, I think RIM is in a tougher spot for phone and OS development. They need to keep the enterprise level security for which they are famous and yet open up enough of the device to give it the "flash" consumers what and the API developers need. I wouldn't be surprised to see OS6 be a corporate and consumer version.