Actually, that is your ignorant take of what Romney has proposed. He says he will lower tax rates by 20%. He did not say he will lower taxes by that amount.
He also says that the tax rate cuts for the upper income will be offset by eliminating the loopholes, deductiona and credits that the upper income taxpayers get.
None of this is cut in stone. I would fully imagine that if Romeny cannot get congress to make all of the necessary cuts in adjustments to income for the upper income taxpayers, he will reduce his proposed tax rate cuts to the levels that keeps higher income tax revenues the same as they currently are. Good fiscal managers modify their stances to deal with reality.
But.....when Obama does the same, he is called a liar, or not keeping his promises? Isn't that like a double standard, or perhaps even a little hypocritical?
Obama doesn't do the same, and frankly, I don't think he knows how to compromise successfully to get a good deal for all. He spent his first two years arrogantly pissing off every Republican in congress, and the next two years bemoaning how those awful Republicans would not work with him on his policies.
BTW, working to get the best deal possible, even if that deal does not reach your stated goal is not lying, or being hypocritical. Especially, when reaching your stated goals requires getting concurrence from a congress with widely diverging political goals of their own. There are two or more sides to every negotiation.
I might truely believe that I am worth a $100,000 salary, but if I can not negotiate successfully to get more than $90,000, I either take what I can get, or go somewhere else.