The most obvious difference at first glance is that in Azeroth, all men are blocky and all women are curvy. Aside from various facial traits, hair and skin color, humans don't vary from this standard mold. Even in advanced age, Azerothian women's breasts do not sag, nor do men's muscles lose their beefy bulkiness. Some Earthlings have disparagingly compared Azerothian men to gorillas for their tree-trunk arms and their "smashed-with-a-shovel" faces, but others point out that Azerothian humans have been hardened through great suffering. Wars with orcs, demons and undead have reduced their population from millions to mere hundreds of thousands, and so the weak humans of Azeroth have possibly been weeded out. So, while many Earthling humans may enjoy the comforts of working at a desk all day, then coming home to play at a desk too (i.e. via computer game), Azerothians, even old ones, have to keep themselves fit to fight off the various enemies encroaching on their lands, such as murloc flesheaters and forsaken undead. While this may explain the over-muscled arms of Azerothian males, it leaves the question of youthfully curved elderly women quite unanswered.
Another difference which may or may not be obvious depending on the Earthling player's background, is that Azerothian humans tend to look a lot like Europeans of the middle ages, and have little to none of the ethnic or cultural diversity that humans of Earth have. Yet perhaps Azerothian humans feel the need for uniformity in setting themselves against the variety of diverse sentient species which have competed with them for the position of dominant life form since the beginning of their world. To this day, these wars for dominance continue, and no clear victor has yet emerged. For Earthings familiar with the images of western mythology, all this fighting and struggling may represent "triumph over darkness", and "surviving against all the odds" -- yet some of us still wonder, "where's the sushi?" Isn't diversity something that should define human beings, no matter what imaginary planet they live on?
One of the largest, yet least recognized differences between Azerothian and Earthing humans is the vast gap in population size. Azeroth is a much smaller world than Earth - Earthlings often have more humans in one city than Azeroth has ever had on the entire planet! Stormwind, as the largest human city, has all of two-hundred thousand people in it (or so they say - I certainly haven't counted that many). On Earth, Stormwind would just barely be large enough to put on a map. This seems particularly ironic, since Earthlings take 20 years or so to reproduce, whereas Azerothians can simply respawn after about 6 minutes. Still, Azeroth is the world of "Warcraft" after all, so perhaps all the war going on is an instinctive response to help keep the population from spawning completely out of control.
We can conclude, based on such preliminary evidence, that Azerothian humans are a distinct species from Earth humans, despite the fact that they share a name. What's your analysis? Are Azerothians simply mirror images of us in all the ways that matter, or are they really a distinct creation? Have you noticed striking ways that they differ from us?