I picked up on this too when I heard Mitt Romney say it recently, but Think Progress, being about 40 people or whatever they are, beat me to it and wrote an excellent post on a very important piece of Romney ambiguation that you need to be aware of.
Romney likes to defend his tax plans and reassure listeners that they aren't tilted toward the rich by saying that under his plans, the rich "will still pay the same share of the tax burden they're paying now." It's very clever and sounds reassuring.
Unfortunately, it's completely meaningless as a measurement of the actual tax burden paid--to measure that, you have to take into account how much X group made before taxes. So for example, as TP notes, from 1998 to 2008, the share of the tax burden paid by the top 1 percent increased by nearly 25 percent. But: Their earnings went up 30 percent. So even though they paid a higher share of the overall tax burden, they actually received a massive tax cut. They just paid a larger chunk of a smaller overall pie but made out like bandits because their share of total income increased more than their share of taxes paid.
The common right-wing comeback that the rich pay 70-whatever percent of all taxes is bogus along the same lines. So what. They have more money. I bet Home Depot pays more in taxes than my local Strosnider's hardware store (although these days you never know). Home Depot has more money. It's a silly and completely disingenuous way to look at taxation, and people like Heritage Foundation wonks know it, they're just trying to come up with some spin to support these class warfare canards.
So Romney is lying, as per usual. He and his aides sat around and thought up the right way to phrase this so it sounds benign and happens to be true. But it's irrelevant, and even worse. It masks the actual truth of the matter, which is that his average tax cut to households earning more than $1 million a year would be around $250,000, and that would be on top of the $140,000 those households would already get if the Bush rates are extended for them, which is what Romney wants.
Think about this, too. If these households are getting average cuts of that size but still paying the same share of the tax burden, then we must be bringing in far less revenue in Mittworld. Yep. Those greedy poor people need a llittle discipline after all.