From what the people hier said the bolded part is not true, because what you get depends entirely on the Leader.
OT: The only way to confirm or deny the rumor of increasing Mount chance, is to actually investigate the drop chance on wowDB or wowhead to check whether it changed since you saw ast. Tried it with wowhead and it is not helpful, displaying "??" as always.
€dit: From the Bonus Coin discussion; if it is confirmed that all who bonus Coin get Mount if the leader coined it; we could have a "clever use of game mechanics" by waiting for the leader to coin and save our own if he did not get it.