$716 Billion (or is it $713?) Medicare Cut

I have been trying to understand this number the whole election cycle, and what it actually refers to. The only thing I can find is this:

"Romney's blog: Obamacare cuts Medicare by $716 billion. Here’s How: Sarah Cliff points out that that number came from, “ …the Congressional Budget Office sent a letter to House Speaker John Boehner, detailing the budget impact of repealing the Affordable Care Act. If Congress overturned the law, “spending for Medicare would increase by an estimated $716 billion over that 2013–2022 period.” So the magic number is the loss in savings if you repeal Obamacare. First thing you want to ask is didn’t we want to reduce our costs?"

Source: On the contary: "It's Simply Not True"

Is this really this simple? Romney and the Republicans are presenting their own plans to repeal Obamacare as a cut made by Obama to Medicare? Am I missing something? Can anyone explain?