As said, a big show to make people feel they have some kind of power and don't decide to change things themselves. How do you get people involved and make them think voting someone is good, give polar opposites to vote for. If half the country think they can vote in someone opposite to the guy currently in charge they hate, they'll take that option . Then when that guy is in charge.... does exactly the same stuff, the other half of the country who hate him can vote for a new opposite guy, rinse repeat. I mean how many people consistently bring up Clinton as the bestest democrat ever, balanced the books, did loads for the working man.... when in reality he brought around some of the worst and biggest changes that led to the financial crisis, while he paid off short term debt while making the long term debt much worse, just to pretend he was balancing the books? He was god damned horrendous, but people believe what they want. Nothing actually changes, the rich get away with more and more(and I'm talking, huge corp's not a guy making a 200k a year working hard), the poor still get nothing, politics hasn't changed, Labour/Democrats keep thinking their ultra liberal leaders are actually making changes to help them.
I don't know who is worse, the people who actually vote for republicans because they are racist and stupid, or the liberals who vote for Obama because they actually think he's going to do anything differently to the republicans.
For the sake of argument, what is better a 40% tax rate for people making over 100k a year, but loopholes mean they can get away with paying 14%, or reducing that 40% to 25%, and closing the 14% loophole at the same time? (I have no idea, and no real reason to believe Romney wanted to do that, and I'm really talking about whats best in the UK anyway).
When trying to pass a vote, in which 90% of the votes are bought and paid for, and 90% of the people voting fall into the "would be utterly screwed" if the loopholes were removed and they went straight to the high tax bracket. Is it not better to accept a middle ground and get quite a lot of extra tax, than keep fighting a battle you can't win, keep asking for 40%, and never get it? Much the same argument as raising taxes on business... rather than pay more, the business just moves away.
Why we don't freeze Ireland out completely until they put taxes up to a "EU average" I don't know. They'll make a crapload of money, if everywhere in the EU changed and charged 20% corp tax instead of basically nothing, the companies that have already moved to Ireland won't save money moving elsewhere, so Ireland will get a hell of a lot more money than they do now(and they need it), and businesses currently in the UK/other EU countries won't see a financial gain moving their headquarters and money to Ireland, so we all stop losing tax as well.
Anyway, politics is a game, the only question is, right now its run by rich people generally pretending there is a chance to change to keep the dumb masses from questioning why the big key things never change.... the question being, was the guy who started it all planning that all along. Much like whoever "created" religion as a way to scare people into behaving well, intentional or just a nut job who shouted long and hard enough that 2 thousand years later people are gullible idiots?