It's certainly plausible. Does anyone really think that these areas went 100% for Obama? If you look at the exit polls, you see actual self-identified liberals who voted for Romney and conservatives who voted for Obama. And yet these areas are 100% unified?
Even if it's not literal fraud, it's defacto fraud. Because the only explanation for such overwhelming homogeneity in the vote, other then fraud, is tribal bloc voting that is fundamentally at odds with democracy.
Why is it so hard to believe one candidate could win 99-100% of a precinct? It's not a huge number of people. I'm sure there are areas in Utah and Oklahoma where Romney won 100% in certain precincts. Is that fraud too?
Just for example, my precinct in 2008 was 453 for Obama - 0 for McCain.