Ah, but now we are getting into the technicalities here. The DWP's case is, in effect, that these weren't genuine claimants at the time (ie, prior to October 2014), so why should they be handing money out to non-genuine claimants? That the guidance subsequently changed doesn't affect that, legally. Or maybe it does.
I suppose the point is that the definition of "genuine" is subjective, both in law and, for that matter, in public opinion. It's pretty obvious that someone who is faking every detail of their claim is not a "genuine" claimant, by definition, but once you move away from blatant dishonesty it gets rather a lot woollier than you are giving it credit for.
It's about your general approach at that point: should the government be looking to help as many people as possible, or should it be looking to give out as little money as possible? At the moment, the current government's approach is essentially the latter. Obviously the former approach is unsustainable also, so you need to seek a balance (and, again, for the record, this decision is IMO on the wrong side of that balance!), but it's not nearly so clear-cut as all that all the same.