This is a bad thing how? As far as I can see, carriers have far too much control over the devices that are used on their networks. I can't imagine consumers opting for devices where carriers have EVEN GREATER control!
It's consumers who buy the device, not carriers.
It seems like a much better position as a consumer to be able to pick an operator based mainly on the line-rental charges and included data, minutes, etc.
I don't know if this is a consequence of laws around unlocking phones or simply because the operators in the UK pretty much match each other in coverage. Most built up areas have even coverage from them all so there is little to lock a buyer into one network or another.
Of course nothing is perfect. Just interesting as a contrast.