[boost] Boost.Threads: Do we need all those mutexes?

Do we need all three separate concepts -- mutex, try_mutex and timed_mutex? I'd expect the mutex concept to remain unchanged and "try" and "timed" refinements to be related solely to the ways I try locking that only mutex. That is, I always have one mutex and under different circumstances lock it unconditionally (scoped_lock) or try locking it and check if that attempt succeeds (scoped_try_lock) or try locking within a certain time period (scoped_timed_lock).