No need to get defensive over the all-american guys now.
I admit I don't care to pay attention much to them, But basically, they all seem to have the same movement, same patterns, same general demeanor, etc.
It's no coincidence to me that the non-college yanks like Harrison stick out like a sore thumb, in terms of individual style. But that's just me.
The only thing that seems to differentiate them is the speed of their serves.
I get what you are saying, but Klahn and Devvarman are bad examples to use b/c they are different as night and day. The college players probably look the same to you kinda like how a lot of the claycourters look the same to me
These college guys, even non-college guys, have similar style that focuses on big serve, big forehand, flat ground-stroke and less on movement aka "American Hardcourt Tennis". They grew up on hardcourt and were taught what works best for this surface (ways of doing things). Even though they share similar foundation, there are still some differences. Johnson tends to slice more than the average Joe b/c his backhand sucks, Klahn is more of a ballbasher than the defensive backboard Devvarman, Williams is more of a dropshot-artist who hits with a lot of topspin, Kosakowski is the oddball with his one-handed backhand etc.