I had wondered about Chief Justice John Roberts' use of taxes instead of the Commerce Clause to justify his approval of the Affordable Care Act. I read somewhere (though I can find or verify it now) that violating a law supported by the Commerce Clause is usually a crime. Violating a tax law means having to pay a penalty (though refusing to pay the penalty is a crime). So not buying health insurance can result in a penalty, but is not a crime.
Ari Ezra Waldman says there is more. Through much of the 1930s the Supremes tossed out much of FDR's New Deal because it said Congress had no authority to make such laws. In 1939, after threats from FDR and a change in court membership, the Supremes began to say, yes the Commerce Clause does allow the gov't to regulate such things as maximum workweek, minimum wage, Social Security, and a host of other things.
But conservatives are fighting back. I'm sure you can figure out why they hate minimum wage laws and other such related things. There was a case a few years ago which asked the Supremes to strike down a federal law that banned guns in schools (though states could do the banning). A more liberal court would have said, yep, the parts of the gun, if not the whole thing crossed state lines so we can regulate it. This conservative court said that gun in that school has nothing to do with interstate commerce. They are trying to reimpose the earlier meaning on the Commerce Clause, and thereby limit the power of Congress. Progressives may have won this battle, but conservatives are winning the war.
Waldman also notes that conservatives are saying if you want the courts to respect the will of the people when it comes to health care (but aren't a majority against the ACA?) you have to respect the will of the people when it comes to the Defense of Marriage Act. Waldman says they're not equivalent: health care is an economic law. DOMA is discrimination.