Obamacare ruling question

So Congress decided to expand Medicare coverage. As part of that bill, they required states to pay for a (small) fraction of the cost of covering the newly insured people. This doesn't mean that the states were being forced to do anything; they could always opt out of Medicare altogether.

Oddly, the Supreme Court ruled this idea as unconstitutional, and allowed the states to "opt-out" of this expansion of coverage, under the idea that the option of losing Medicare entirely was too large a penalty, making the bill "coercive". I can't wrap my head around this entire idea. Does this ruling mean that the Federal Government is now required to give this level of Medicare to the states without any modifications for the rest of time? Common sense says no, but wouldn't any changes in the policy be just as "coercive" as this one?

Typically, with these rulings, we hear only the super-simplified versions of rulings, so maybe I'm just hearing a stupid version of the argument. As it is, I just can't understand why the states are entitled to Medicare now, and the Federal Government is no longer capable of regulating the rules under which it spends money if the states don't feel like it.