There are very few character concepts I'd be interested in playing that couldn't be done with a human character. If race had no mechanics, then my choice of race would have to have really interesting story/lore implications for me to bother - I might still play a Warforged in Eberron, for example, because what they are about and their place in the setting is intriguing.
Elf? Nah, I can play as a graceful and beautiful human who is good at magic.
Half-orc? Nah, I can play as a big strong ugly guy who's a human.
Dwarf? Nah, I can play a short, bearded miner who loves to drink and is a human.
Halfling? Nah, I can play an even shorter farmer who loves to eat and is human.
Gnome? Nah, I can play as a little old man who does magic and is a human.
Centaur, since there has been a lot of discussion about them? Nah. I'll just take my human and stick him on top of a horse.