The reason why the old-timers around here are sticky about this is that we believe we are writing for the mailing list archives. Gmail-style quoting is indeed the appropriate amount of effort for throwaway threads that only a few people will read and (probably) none of them will consult again later. But for threads that (a) will be read by hundreds or thousands of people right now, and (b) will be searched for in the project archives some unknowable number of times in future, it is worth spending extra effort to make the conversation easy to follow.