Headless Horseman's mount was also increased back in 2010(?) or 2009, 99% sure it was 2010. Was like a 1/500 drop chance from the boss prior to the loot bags, now it's like a 5% chance.
It honestly wouldn't surprise me if they bumped up the world boss drop rates eventually, as much as it would make me sad since everyone would have the Sha mount (yes I'm a special snowflake that has it and I want to remain special), the drop rates are absurdly low, I have seen a grand total of two world boss mounts drop out of the thousands of people I've grouped with, one of them being me. The other was some dude that got the Oondasta mount which seems to be considerably less rare than the other 3 world boss mounts. One of my guildies has the Galleon mount too, not seen anyone else with that but that might be because it's a ground mount.
However, a mount that is definitely justified to have an increased drop rate is the Love Rocket. That thing is absolutely ridiculously rare considering you have a two week window pr year to farm it. It's fugly too, no idea what they were smoking when they made it a 0.2% drop chance...
On topic: Got 202 mounts atm, have quite a lot of vendor ones that I haven't brought yet though. If I'm not including Alliance mounts, I should have 212 just from class mounts + Pandaren Phoenix's & Emerald Drake, will probably buy the other vendor mounts, Vial of the Sands etc to get 250 before WoD releases.