Yeah, curving has it's uses in many games, but for Smashball I think it's working okay. Keep in mind that adding something like that to the ball will only increase the massive amount of packets required to keep the game updated, and a ball moving at a default trajectory is far simpler than trying to update it with spin. It's already hard enough to shoot accurately at high speeds; if you're flying to the left in front of the goal at high speeds, you have to aim like 45 degrees to the right just to get the ball to shoot toward the goal. The momentum of your body effects the ball, just like in real life, and if this game were in real life, I doubt you could spin a ball of this shape/weight, and with those massive padded gloves they wear
It's all part of the realism.... But than again, the passing...