Is there a diffrence in game quality when you DL over the internet VS buying a disk?
There is no difference as long as you BUY and download, not download pirate copies. Whether the game is sold online or on a store shelf, it's the same piece of software, so why should there be any difference?
If you buy a lollipop does it taste different whether you walked to the store or drove to the store ? Whether the game files are copied of a CD / DVD or downloaded, the end result is the exact same set of files on your HD.