Both Clinton and Obama has not made any distinction on the inducements they make for low income folks to opt in to the system. Since on the offer of subsidies in either plan is essentially the
same, I don't see how Hillary has "won over" low income people that
Obama hasn't.

There are two categories of people who can be left out

1. those that don't want to buy insurance even when they have a good enough income to do so.
2. Low income folks who cannot afford it.

Wherever I see there is no clear argument or estimate of how many there will be in either of these category.

Clinton claims that everyone is mandated to buy insurance and has not spelled how these mandates will be enforced. Its clear her mandates would technically be possible on the folks in Category 1, but needs to be spelled out for Category 2 for whom this can be big blow. Clinton if I understand right, claims folks from category 1 will provide and subsidize for folks in category 2.

Obama is wary of folks who will game the system (Cat 1) and is open to penalties. What those penalties will be is not spelled out, although such an enforcement is technically possible. Obama can then potentially use enrollments from Cat 1 to offer further subsidies to folks in Cat 2, just as Clinton argues.

So Obama can get away with providing essentially everything Hillary plans to provide with some weaker form of mandate which he calls penalties to gaming the system. At the least, in Obama's plan, if you didn't buy insurance and
the income is really low, it won't be grounds for penalty. At the same
time both Obama and Clinton can offer the same inducements of subsidies
to low income folks to make it possible for them to buy health care if they chose to.