In another comment thread, I wrote:
In order for the Court to have standing to hear the suit—because if it were a tax, it could not be heard until the “tax” kicks in, which I believe wouldn’t be till 2014—the Court had to consider it not a tax, which they did. They determined that for that purpose they would go by what Congress called it. However, for the purpose of deciding on its constitutionality, they would switch hats and call it a tax and therefore constitutional.
Sort of like light is sometimes a particle and sometimes a wave. Except this isn’t physics.
On reflection, though (and with a little nudging from Artfldgr), I think it’s actually more like this: