Does the near "tie" between Repubs and Dems mean anything?

I have a theory - and I've been too lazy to spend more than shower time considering it - that there's a fundamental reason that US elections come up so even election after election (yes, Obama is crushing McCain in the electoral college, but the popular vote is pretty close... and it has been pretty close - with some oscillation back and forth - for a long time), and that that reason is that basically that they are both equivalent. I don't think I can prove that this virtual "tie" *has* to be caused by this "equivalency", but I suspect that you could make an argument that *if* you had more or less equivalent parties, it would result in the election pattern that we are seeing.