The weight is not going to be an issue with SuperDISH. The larger dish is going to catch more wind and therefore transfer more force to whatever surface or object it is mounted. The increase in these forces is why it has a beefed up pipe, mount, etc. For this same reason, it will be even more important to mount the dish solidly. The dish itself will not be more prone to damage, but it will be more prone to damage whatever it is attached to in a high wind situation.
Most likely the reason DISH is leaning toward professional installation is simply the increased complication of aiming at three targets.