This has always been the case. They don't always do it, but they've always stated that they can. As the number of people opting for hand baggage only increases (normally to avoid paying to check in a case), the problems with not enough overhead locker space increases, so they know when to start measuring the hand baggage - not to make money (although they won't mind that) but to reduce the amount of bags getting into the cabin to ease the storage problem.