You've quoted from Connecting Threads.. I really love Connecting Threads and buy most all of my thread from them and other things as well.. but I think they are like most 'quilting' establishments.. they want to sell you fabric to back your quilt.. and they should, that's their business and their livelyhood, they would be poor business people if they didn't do what they could to sell their product!
I agree that high count sheets might be a problem, in theory anyway.. but the looser (cheaper) ones are not a problem.... I've used them and never had holes or any other problem..
That said, I once backed a quilt with Batik, which is very tightly woven, and still have no problem.. So I'm not convenienced that it matters a lot what you use.