I'd say the majority of us watch real tennis...now most of us probably don't play it (I do) but I think most of us watch it.
Anyways you are right dazzer, almost every shot in real life has some amount of sidespin...I was going to say something but I just looked back in the topic and that bastard Rob has once again said EXACTLY what I was going to say

So just read what he said again.
I just don't think it's that big of a deal TBH. There is sidespin on almost every shot but with most players it's not enough to really change the trajectory/path of the ball all that much. I think it would be a lot of work (to implement in the most balanced way possible) for something that wouldn't affect gameplay all that much in a positive way.
regarding your comment about TS2 having the sidespin button...that button f***ing sucked. It was guaranteed to go in and most people would just save it for a time when they were really stretched wide and needed a guaranteed ball in the court. I used it of course because it was in the game, but the Momentum Shots in TS2 were corny as hell.