I did check the Clothide (I think that's correct) site about their thread information and found this quote:
Fiber: Try to match thread fiber to fabric fiber. Cotton fabric should be sewn with cotton thread; polyester or manmade fiber should be sewn with polyester thread. If possible, don't sew natural fibers with polyester thread. Polyester fiber is stronger than most natural thread, so over time, the stronger polyester thread can break the weaker cotton fiber of the fabric. For quilting, look for thread labeled "machine quilting" or "hand quilting."
So, polyester thread is available to all of us today.... I just don't buy any of it for quilting due to its strength. It is still okay for polyester fabric.... but I don't buy any of that....don't like the feel. There are still plenty of those iron-strong quilts made back in the 1960's from polyester knits..... really don't like those but I hear they are warm and wear like nothing else.