American academies are the main antagonits for tennis stroke development. I mean every up and coming kid is 'nurtured' in the same robotic, mundane way. I'd rather have the unorthodox technique and the 'conventional'. Could you imagine Graf or Federer with 'standard' forehands?
Players like Ginepri, Reynolds, Isner, are examples of this.
Isner did not learn to play from an academy. Regardless of where he learned to play, though, his game would most likely be similar to what he does now since he's limited by his size.
Incidentally, neither Blake nor Querrey grew up at academies. Roddick and Fish went to high school together (a traditional one) and spent time playing with other top young Americans in the Boca Raton area. To my knowledge, the group they played with only learned from one coach, but it was more like just a traditional tennis club than an academy.
Americans having similar games is more a product of similar courts (fast hardcourt) all over the country and most juniors growing up playing on these. This is changing, but it will take time. Young, for instance, does not have the "normal" American game. There's no need to develop beautiful backhands and volleys and how to construct points when you can just hit a big serve and forehand. This logic wasn't flawed until the courts began being slowed down over the past decade to make the game more interesting to watch. American tennis has to respond to that, and in my opinion it is. Patrick Mcenroe, who is now in charge of junior development at the USTA, actually just had a conference call with reporters outlining the changes he will be making to respond to this.
IMG/Bollettierri's academy has done a lot to popularize the aggressive baseliner game beginning with Agassi, but none of the top Americans, men or women, learned to play from him when they were teens. I don't know how his school compares to some of the major European ones.