Hi herc, which new forum did you join? Well, I suppose since there aren't much activities tenniswise these days, the discussions are bound to get like that.
Sampras was 6'1" so I don't think height is what required as far as the serves go. Sampras 2nd serve involved high risk but then again he had a lot more confidence in it so it worked out for him most times. I don't think Andy feels as confident about his serves especially about his 2nd serve. He's usually a bit conservative with it.