Not all members of a given race act the same, but in the game and in settings you do have a need to have an elf act different than a human otherwise the elf is just a human with pointy ears.
Frankly, I think settings like Wheel of Time nail it. Humans are slightly different and have their little bonuses and penalties, while the real alternate race is VERY different. However, I do not run the world, more's the pity because I'd get rid of that weird yellow moose on the Noggin network.
Humans tend to be the baseline.
Elves tend to be "cool" humans
Half-Orcs tend to be "thuggish" humans
Dwarves tend to be "dour" humans
... which leaves halflings and gnomes both contending for the same archetype of "short"
I like what Eberron did with halflings. I don't like what Eberron did with gnomes. Hold that thought. I like Eberron's Warforged. I don't like Eberron's orcs. It's the same problem. When they introduced Warforged, the half-orcs got marginalized. Likewise, I've seen a lot of settings do cool things with halflings or gnomes, but not both (unless dwarves get punted to the side or whatever).
In any literary work you don't add crud just for the sake of adding things. Typically, I see races added that just don't do anything. They're just there for the plusses, minuses, and nifty artwork.
Happy gaming!