Hi and welcome to the board.
I have an Innova and my 10 ft table (aka a rack) is 10 feet from outside edge to outside edge. But I have less than 10 ft of available quilting space. Room at the sides is taken up by the supporting structure of the rack and you also lose space from the machine head itself. You also want to have room at the side to change bobbins and attach side clamps. So yes, I would say the Prodigy explanation of available quilting space is pretty much spot on and pretty universal to most rack setups. I don't like loading anything over 100" on mine.
As far as professional quilters getting quilts wider than 102" I have had to turn down several jobs due to my restriction and I really wish I had a larger rack to load some quilts sideways. Most King size quilts are wider than 102". If you can squeeze in a 12' rack in your space do it! I wish I had but I would have been very hard pressed to get a 12' rack in my dedicated room.