"I have yet to see a wild pitcher suddenly have command but have seen pitchers go from 87 to 90."
You need to get out more. This happens all the time.
Personally, I believe that sound mechanics enhance both velocity and command. A kid who is already showing a live arm often just needs to fix his delivery in order to pound the zone.
I've also seen conditioning work help with great frequency. If a player is tiring after 70 pitches, he can be off 1/8" in his kick position, which makes him off 1/2" in his release angle, which makes him off by 12" at the plate. Build up the core and lower body support muscles and those problems go away, while the live arm is still there.
Not every live arm gets fixed, and for that matter, lots of players with natural talent lack the work ethic or the mindset to prepare fully and then compete even when the going gets tough. Some guys are really good at avoiding the strike zone for fear of giving up hits.
And yes, guys also gain in velo over time. I see that all the time, too.
But the guy who throws harder is typically the higher prospect because the upside is higher if you can fix him. And high level coaches typically have a lot of confidence in their ability to teach. (Even those who aren't really good at it, have that confidence anyway!)