I think the IDS resignation is more to do with political manoeuvring than a difference on welfare reform.
It s well known that the Conservative Party is deeply divided over Europe, and IDS and Osborne/Cameron are on opposing sides.
If we vote for Brexit, there are many who think the Prime Minister, and by default, his Chancellor's positions are untenable and that a leadership challenge will unseat them.
It is also well known that Osborne and IDS do not get on well. So when Osborne dictated that IDS must make £1.5billion annual cut, IDS went away and thought of the most unpopular cut his department could make, that of taking money from Diabled people.
Osborne put it in his budget and is deeply damaged, with Tory MPs rebelling left, right and centre. IDS then resigns and publicly disowns the policy that he designed.
He can now become a leading Brexitter, and if they win the referendum, and Cameron is out on his ear, he is well positioned for an even better job.
That to me makes more sense than IDS is suddenly a crusader for the disabled poor.