everything you wrote makes sense, providing larger labs like the MSL cannot be delivered by the ballistic-bounce method used in MER and Pathfinder. Is this the case? Then Skycrane would make sense. Otherwise it would seem to be a validation exercise for the Skycrane - which would seem strange given the cost, and (as you point out) the superb record of Nasa so far, on Mars. They must already have a huge amount of data so far on the Martian gravity profile and atmospheric profile and presumably MRO is going to add to that and refine it with much greater resolution.

But I repeat, your discussion on the need for larger landers and more precisely targetted locations, only makes sense to me only if MSL can't be delivered via MER methods. I also can't see how Skycrane is going to give greater targetting capacity - it's reserved for the very final stages of EDL, so I imagine with good, fast AI it will still only allow for a more exact choice over a very restricted surface area, probably of some few hundred square meters at the very most I would have thought.

So, maybe Skycrane is all about delivering heavier and larger landers, more safely than the MER methods.