I think part of it has to do with the ease of obtaining gold over the years. Back in vanilla, it was an incredibly long time before you saw that first gold piece. Saving up for an epic mount at level 60 was almost a rite of passage. Hardly anyone I knew had enough gold to get one when they actually hit level 60; they had to work at grinding enough to afford the mount. And racial mounts were racial mounts. You couldn't get a horse if you weren't human, and you couldn't get a raptor if you weren't a troll. When that changed, it opened up opportunities to actually start collecting -- and when gold started getting easier to obtain, especially through the addition of daily quests, the means to collect got substantially easier.