Indeed, people always stick to the microcontroller he/she familiar with, including me. However, I think this is not suppose to be the main factor that determine which microcontroller to be used.
If a new microcontroller offers more powerful function and performance, you will have to consider to use the new one. Otherwise, your product may be eliminated from the market.
Apple doesnt use Motorola anymore, most of the computers use Intel; getting more ppl choose Nokia, Samsung cellphone instead of Motorola. However, motorola microcontroller is still playing an role in embedded system. I guess there should be some other reason behind this, isnt it?