I dunno, they're faster than not having a mount, or one of the actual vanity mounts that don't increase your speed at all. That's what counts, they're functional, and you pay real life cash to get one, instead of in game gold. If CCP offered a ship, say a Rifter or a Machariel with a different skin for sale in Noble Exchange, would you call that an non-functional vanity item?
I think it's slightly different. I looked at the Blizzard store page for the purchasable mount and it states "... and it will travel at 310% speed if you have at least one other 310% mount." I take that to mean, "you can use this mount if you already have the normal in game 310% mount." So if that is the case, it is purely a vanity item as it requires a prerequisite item with the same stats that is acquired in game (my assumption). It isn't the same as a ship in EVE because ships in EVE can be lost, WoW mounts cannot. So basically you're simply buying a skin for a mount, and not actually getting anything "new." Now, if my assumption regarding needing an only in-game obtainable 310% mount as a prerequisite is wrong, then yeah, it's far more similar.