I got involved, slightly, in a discussion about fantasy races on a discussion forum dedicated mostly to Dungeons & Dragons. This issue is always a little bit of a pet peeve of mine, in that I'm always surprised how many people cannot seem to get around the mindset that the standard D&D races don't have to be used.
That was the main question that sparked the discussion, and was followed up with a slightly hapless "well, if I don't use elves and dwarves, what do I do instead?" The main reason that this always surprises, and quite frankly disappoints me, is that fantasy fiction settings rarely assume that there are humans, elves, dwarves, halflings, etc. That's a latent Tolkienism, but other than Tolkien, few other writers did anything like that. Until D&D came along. Even now, though, few authors except those that write D&D pastiche fiction, official or otherwise, assume that racial mix-up. Many, many fantasy writers assume a baseline of human only, from sword and sorcery Fritz Leiber or Robert E. Howard, to modern high fantasy back-breakers like Terry Goodkind or Robert Jordan. If other races exist, they're strange magical creatures, most often, not something that's "like a human, but not."
And as a person who came into gaming through the avenue of fantasy fiction, emulating the feel of said fantasy fiction is important to me. If the Hyborean Age works with just humans and monsters, then so does my fantasy setting. That said, I do like to add a few exotic touches here and there. In some settings, I've merely made exotic humans. I think I got the idea from Edgar Rice Burroughs, who had his red men of Barsoom (as well as his other "alien humans") but the idea is based on science. If humans are adapted to Earth, and endemic to earth, then the specific ethnicities that we see are also endemic to Earth. Put humans on some other planet, and let them have it it for a few hundred generations, and they'll probably develop into completely different ethnic groups altogether, who don't necessarily resemble Earthly ones at all.
This is perhaps too "science fictiony" a concept for a lot of fantasy fans, who want "mytho-historical resonance" out of their fantasy, and therefore don't mind at all that their fantasy kingdom is almost exactly like the vikings in every respect, or whomever it is that they're imitating.
For those kinds of tastes, I don't mind borrowing some ideas from D&D... just not the typical ones. The last setting I came up with specifically disallowed elves, dwarves, halflings, gnomes and half-elves. They simply didn't exist. I didn't disallow half-orcs... and if half-orcs existed, then so too did regular orcs. Make goblins and hobgoblins into a playable race, an LA+1 variant of tieflings and fire genasi, and shifters and changelings from the Eberron Campaign Setting, and I was all set. Plenty of options for players to pick from, and yet a very different feel than regular D&D. Since I've set that game in Freeport, and it specifically has a political intrigue, swashbuckling and Golden Age of Piracy feel to it, I think that grafting Tolkienesque conventions probably wasn't the best idea anyway.
And that's one of the things that I actually quite like about a mature, robust ruleset like D&D. Although there are things I don't like about the rules, one that I very much do like is that I've got a very full buffet of options to choose from when creating a game mileu. You can really significantly change the feeling of the game by removing some of the default options and putting some others in instead... even without changing anything else about the system.