Is SC2 aiming for quality single play?

Partially. But like I said: I find it hard to believe that only the multiplayer will have multiple difficulty grades. Warcraft 3 had two, but since they are really focussing on better AI, it would be strange if only the multiplayer would benefit from that. Like the workers running into artillery style fire all the time, instead of using transport units. That could still remain in easy mode and removed from normal and up, for example.

@ Necromas
We have a whole thread on this, you know.