This could be a harbinger of a two-trip wonder. (Two trips before the USSC, like campaign finance reform had to make.)
The first trip called it a tax but did not treat the question of whether it was a constitutional tax.
The second trip will treat said question.
Maybe that was Roberts’ intent: to set up the possibility of a second court decision on the constitutionality of the Obamacare tax. Limit the commerce clause in the first go round, then knock down the tax in the second. Seems to me that he should have done both since, as someone pointed out earlier, the kinds of taxes the federal government may impose are spelled out pretty clearly, and taxing non-activity (e.g. not buying health insurance) isn’t one of them.