They are, but they're doing it differently than the Army and the Air Force. Instead of just replacing all their M9s and the Corps' M9A1s, they're only replacing pistols when they reach end of life cycle, so the Corps will have their A1s until the mid 2020s according to the last report I saw.
As far as I'm aware M-18s are only with Security Forces at this point. Still think there are M-9s in the inventory for aircrew. This thread has peaked my curiosity so I'll check in with AFE next week.
11 million for 125000 pistols, that's $176 each.. Sounds like a deal IF they run like they're supposed to..