I think the interesting point is that they are now bound by it, one way or another.
Given that, it makes sense that they'd support the notion that all other competitors be required to do the same. I don't think this is particularly altruistic in that light.
I would agree if it were not for the fact that they are only bound to the Open Internet Order until 2018.
They also did this while fighting it in court. The Verizon suit which struck down the Open Internet Rules only came as a result of a previous Comcast suit.
Given that, it makes sense that they'd support the notion that all other competitors be required to do the same. I don't think this is particularly altruistic in that light.