For d20, I guess humans are convenient as a "base" race, having no modifiers, and thus the basis for comparisons.
IMC, 3 of the four major continents are not dominated by humans, although their presence is increasing in each. On one of the continents, a goblinoid race ( big suprise huh? ) is the culturally dominant humanoid race. Detailing the societal structure has been challenging, radically altering stereo typical goblinoid roles.
Obviously, it's much more difficult to use store bought material for detailing/adventuring in the non-human lands. That's no big deal, but because of my different approach, it has often caused me to reflect on why most fantasy worlds are so human centric. In fact -Most published campaigns/sourcebooks/adventures are really NO different from each other - by design. It's easier to integrate, and share between settings.
I really enjoy the diversity that D&D ( and especially now with d20 ) allows. I first became fan of the Planescape setting, because it allowed me to get out of the Human/Elf/Half-Elf/Dwarf/Halfling/Gnome ( & usually in that order ) box.