Note that coachld speaks of taking his cues from "the best in the business" and not just any generic, so-called "professional." So, I think he means those who have shown proven results with their methods. As to the correlation with strength numbers, while I'm not sure you can make a strict correlation with individual strength stats and velocity numbers, I no longer doubt at all that strength gains through lifting can accentuate other pitching work and aid in velocity increases. Now, you're not going to just bulk a kid up who isn't also working on pitching and turn him into a fireballer, but take a pitcher and put him on a good lifting program and it will accelerate increases he will already see. Not to mention very probable durability and health assistance.
I, for decades, bought into the whole "pitchers should stay away from weights" thing. I no longer ascribe to that now that I see the results. When I first moved to this small town I now live in four years ago, things started changing for me in that respect. I live in Lamar, Co - population less than 8,000 and not another town that big within a two hour drive. This is truly the sticks. However, the first thing I noted was that this little school had put more players in the major leagues than all but two schools in the state - most notably Doug Brocail (current Rangers PC) and Scott Elarton. When I did a little research, I came across an article from 1991 concerning the coach's (Jesse Downey) success with developing pitchers who threw hard. What baseball magazine did I find this in? None. It wasn't a baseball magazine, but rather a weightlifting publication. This guy, while almost every coach at the time - including me - was teaching that weightlifting was horrible for pitchers and mobility - had his pitcher doing Olympic weightlifting. Hmm. Thought it was worth a shot. Since that time, pitchers I work with have been healthy, thrown harder, etc. I see velocity gains into the low/mid 80's that I sincerely believe 15 years ago I would have struggled to get to the high 70's. Just my experience.