Well, in 2005 our first HS pitcher taken was in the 15th round. We did take Willems and Gibson in the first 5 rounds in 2006, and Smoker in 2007.
The guys from 2007 are still only 21, so while I agree with the proposition that we haven't done real well with HS pitchers there's far too few data points to say the failure was on development rather than scouting. As far as I know, Willems didn't have the stuff or the head we thought he had, and Gibson and Smoker can't break 90, can they?
I always thought our problem was with Jimbo's scouting profiles (i.e. paying too much attention to fastballs as opposed to overall makeup and secondary pitches, or focusing on athletics and projection over in-game plate discipline and power) rather than development. It's hard to develop players who actually aren't that good to begin with.