Remember how Bush fought for and won all sorts of tasty tax cuts for the very wealthy? No one ever said that those cuts had to be "revenue neutral" -- they were not offset by either spending cuts or other revenue sources.
But if a tax affects the middle class -- as, increasingly, the AMT does -- than any "reform" means "revenue neutral." The middle class only gets a reduction in one tax if they pony up more in another tax. The Republican Congress would certainly never cut spending on pork, so it's up to the middle class to bend over and take it.
http://www.nytimes.com/aponline/national/AP-Tax-Overhaul.html