I think that the quick answer to the original question is that sims are very effective in getting you going with RC flight, but not in making you an expert flyer.
They are great fun when you've got a little spare time and bad weather.
I myself learned a lot with a sim, however I'll never be an expert flier ( who cares? - great fun).

EDIT.

SP2Pilot, you got it pretty right, - well said!