I'm not sure why you are convinced that this election will be an exact repeat of 2008 regarding who goes to the polls when, but I guess we'll know soon enough.
Because, unlike 2008, Obama has a record. And it SUCKS. Therefore, you have lower turnout (particularly among younger voters and black voters).
And, with the whole novelty of electing the first black president now gone, it's safe to say that Obama's turnout will NOT match the 2008 turnout (the early voting numbers prove it).
Obama won Ohio by amassing a HUGE lead in early voting (over 340K). McCain got more votes on election day. But, that lead of Obama was too massive to overcome.
Now, he only leads Romney by about 75,000 or so. If GOP turnout even matches what McCain got, Romney overtakes Obama and wins Ohio.