The droprate on mount was 'extremely' low last year. Did it each day with x5, didn't see any mount. The fact that almost everyone at 80 does this boss, and afaik i only saw 5-15 MAX of these a day in shattrah should tell you that its really low. Ofcourse everyone don't use that flying horse, but back at 70 i guess almost everyone who got one used it atleast during the event.