That may be true, but the fact that Blizzard can't stick to their storylines makes me have more than a little doubt. They've really ruined what could/was a beautiful story, complete with a good plot. If they can't maintain continuity and avoid serious loopholes, conflicting facts, and other such biazzre fuck-ups when making the game expansions, why trust anyone to be about to make a good movie with it?
Furthermore, how can you say it would be easier for people to identify with humans and night elves over orcs and trolls? I am pretty sure there is a large percentage of players that more than readily identify with their characters, regardless of chosen race.
Besides, look at other movies that have gone over really well with strange main characters. They don't always seem like they'd be likeable, affable characters/races/whatever.