Well, technically true, but the hypothesis is that there isn't enough organization in the world to bus so many inner city people to the polls at the same time, so they spread it out over weeks.
I know your point, but while Obama still would have won in 08, it would have been very close in a lot of states without early voting because these are not, as they say, "high propensity voters."
Ofcourse, EV is important to Democrats because of the issue of making sure they vote.
Ultimately however if the GOP turnout is high enough it will beat the Democrat EV.