Case in point: Canon’s new XD series to their longtime X0D DSLR models.
Lars Rehm and Richard Butler on Canon EOS 7D:
At first sight the 7D looks a lot like the EOS 50D and is unmistakably a member of the EOS family. However, a closer look reveals that on the new model Canon has made a few seemingly subtle changes that nevertheless make a difference in terms of handling and operation. The buttons are larger than on preceding models. These changes to the control layout, alongside the custom control menu, gives you more than enough options to fairly easily tweak the interface for even the most specialist requirements and applications. The same is true for the new AF system which offers an abundance of AF point selection and focusing options.
Read: Canon EOS 7D Review
PS. Talking about changes, rumor has been going around that Ricoh is about to introduce a significant update to their popular GRD lineup, engadget has some more info and pictures on the exciting new system.