Papa,
No guru here! But here’s my opinion.
Some pitchers throw with less, some with more velocity by the time they reach the top.
The stadium readings are more accurate in some places than other when compared to the Stalker. I believe most use a Jugs system, but it is far from the little hair dryer units people carry around at games.
Hype does not get someone to the Big Leagues. They don’t pay first rounders millions of dollars based on hype. Yes you are correct, in most cases where velocity is slower it’s because the pitcher has learned how to get hitters out. This would include one, or more, of many different reasons including better movement, more deceptiveness, better pacing for starting pitchers, better command. Then there are the Bobby Jenks types who throw harder than ever now. Often these guys who throw harder now than in the past are relief pitchers.