I think the most important part of pitcing, other than the obvious abilities to locate and change speeds, is movement on the fastball. There are so many examples of pitchers who use this ability to incredible advantage.
Roy Halladay had a 98 mph straight fastball, and got shelled. Now, he throws it 93 mph with great movement and he's a Cy Young award winner.
Esteban Loaiza has always had great stuff, but has never put it together. Last year, he learns a cut fastball and he's one of baseball's best.
Derek Lowe has great movement on his fastball, down and in to righties. That's what gets him so many groundball outs (and called third strikes against the A's in the playoffs ).
Mariano Rivera, perhaps the best example, has one pitch. A fastball that cuts about a half a foot. Throwing only that has allowed him to be the most dominant closer for years.
My question is this...Why don't more pitchers try to develope moving fastballs? All that's required is slight alteration of grip, fingerpressure, or arm angle, none of which are that hard to do. If I was a pitching coach, that is what I would preach.