The explanation I heard was that any means of enforcement of illegals not having access was removed. Something like that, I didn't catch the whole explanation. I guess I could try to search for it.
Originally, illegal immigrants were prohibited from receiving the affordability credits. (tax credits for people of modest means need to buy health insurance) They would probably still have be able to purchase private health insurance on the national health insurance exchange. However, that is essentially the status quo; there is nothing currently prohibiting illegal immigrants from purchasing private health insurance.
However, Obama just now (last night? whatever, saw it somewhere recently) said that he wants illegal immigrants to be prohibited from using the national health insurance exchange, which is more than the Republicans wanted.