I'm still going to say that defense looks a little bigger on that then it is. For one thing, some of that is honest to goodness war related defense of the type that actually helps protect soldiers in warzones. Knock 160 billion off that tag as war related or "war related". That type is going to get phased out as the wars draw down so there's a small blessing. Then keep in mind that another chunk of that defense stuff is soldiers pensions, tricare, etc. The remainder is the actually discretionary spending; current salaries, procurement, contractors, etc. The point as I see it is that discretionary defense spending, while the biggest discretionary item, isn't too big when compared to the 2/3rds of the budget or so that is non-discretionary or impossible to dodge (i.e. interest or warzone spending). It's certainly not the only important point, it's just the one I like to make. Defense is big, but trimming the fat and pork out of defense isn't enough by it's own.
The other fun point about discretionary funding is that the GOP has set it's sights on trimming 65 billion out of that orange slice of yours. So basically they are cutting 10% of everything we actually think of as government services once you get rid of the cash transfers (i.e. pensions, interest and medical insurance). So everything the government does except shoot people feels the pain, education, conservation, postal service, transportation, law enforcement, welfare, unemployment, the IRS, etc. And even within that they've spared pretty much every scrap of pork (like farm subsidies to millionaires) while homing in on the social welfare (like food subsidies).
But yeah, like you said, the Medicare system is really, really broken. It's a simple problem of medical cost inflation. Medical inflation is far, far faster then economic growth rate. And that isn't just a problem for government but is a problem for the economy as a whole. So what's really needed is some sort of aggressive cost controls. The good news on that was that a lot of the less publicized parts of the health care reform bill were trials to test out a bunch of different things to reduce medical inflation. Some of them could work and if Medicare resists medical inflation, it's large market share makes it likely the rest of the country will follow suit. The bad news is that the health care industry really hasn't picked up on the fact that they are bankrupting the country. In an ideal world, we would be aggressively considering more healthcare reforms to address this very pressing problem. In the real world...