The idea that both sides, in many respects, are two sides of the same coin rings pretty true overall, but there are big differences imho, that affect people differently. People vote for what is in their best interests and the interests of their families when all is said and done. At a presidential level, the coin analogy is somewhat true. Take Bush to Obama...Guantanemo stayed open, tax cuts remained, Afghanistan remained in play, corporations got pandered to but just in different industries (Bush sucked up to Haliburton, Obama to Solyndra), and so forth....but when it comes to entitlements, they differ greatly and I don't feel they are two sides of the same coin. The GOP would like to close the social safety nets, especially SS and Medicare, and at the very least privatize them. The Dems don't want that at all. Environmentally-speaking, there is little in common between the Left and Right. Where immigration is concerned, they both really are not much different. The Left likes the Hispanic loyalty to their party, the Right likes the cheap labor in the ag. and service industry plus the Hispanic patronage of superstores and their goods. Defense-wise, the Left seems more police-oriented wanting to be defensive and drone-driven, sanctions as policy first, the Right likes boots on the ground and sabre-rattling, boasts of strength and force. The Left is abortion-pandering, the Right wants to restrict it tightly (which I like). The Left is driven toward a gay rights agenda, the Right firmly opposed to it. The Left is pro-gun control often to extremes, the Right is often TOO unrestrictive.
I think in elections there are net gains and losses not matter whom you vote for. As a teacher, I hate the social policies of the Left often times, but find their union patronage and protection of our rights to collectively bargain important. In my State, the GOP just sought to put a strangle-hold on our ability to lobby for our union, giving the sole power to do so to corporations. Luckily, it didn't pass. The Right is very anti-union, the Left the opposite.
So I get what you're saying about big ideas like corporate hind end-kissing and several other large global issues being two sides of one coin, but really the election does indeed change the fortunes of many. I do believe that. Ask the teachers in Wisconsin. If both sides really came out the same all the time, the lobbying that goes on with abandon in this country wouldn't be in play. Money talks and __________ walks, as they say. And you have to follow the $$$$$.
Passions around the election arise from a strong belief that the vote represents real power and that changing the person in the chair will really change things.
Those that notice, over time, that a victory of the supposedly opposing party does not result in the repeal of the other party's laws gradually cease to believe it.