Frankly, a level 70 on a non-epic mount isn't all that rare. My level 66 rogue is still riding around on a slowpoke Undead pony (just because he's an alt I was never willing to spend that much money on), and lots of Paladins and Warlocks just never got the chance or resources to get their epic mount quests done. For a main, it might be a priority to get a fast mount, but for alts, most people are usually pretty apathetic about it.
Not that there are any excuses any more. With money flowing the way it is in Outland, 900g is no more than a few days' work. And while a flying epic mount is really the best for gathering professions (nothing more fun than dropping in, grabbing a mine node, and jumping back into the air), an epic ground mount really helps with both grinding and questing-- the faster you get somewhere, the sooner you can start earning XP. Not to mention that for the BGs, it's practically a must. Not having an epic mount after 60 doesn't make you a total freak (Malleus didn't really need to take a picture), but there isn't any really any excuse not to get one either.