a d10 is a 50% chance of success for Exalted characters on average, because they get 2 successes on a roll of 10.  on average, 2 dice = 1 success.  You can't ignore doubling successes when calculating that average -- and Combat benefits more than anything from doubling successes.<br/><br/>having to spend 10 motes for 5 automatic successes is not as desirable in combat as spending 5 motes for 0-10 successes because if you run out of motes you die and 10 motes is a lot of motes.<br/><br/>if you know your target number is going to be, like, 1, sure, spending the 2m for the automatic success is easier.