Maniac, if you saw poly thread cut threw quilts it wasn't because the thread was poly, it was because the thread was stronger than the threads in the fabric. From Knitette's link:
Will polyester thread really tear the fabric in my quilt?
Thread will not tear through a fabric solely due to its fiber content. If a thread ever tears through a fabric, it is because it won the strength contest. In a battle of heavy use and high stress placed on a quilt, the strongest component will always win. It is not accurate to say that a polyester thread is stronger than cotton. I have a spool of thread on my desk labeled 100% cotton quilting thread. It is a very well known brand, widely available, and is one of the top selling machine quilting and piecing threads. It is twice as strong as a comparable polyester thread. Although it isn't labeled as such, it is coated with a glaze which strengthens the cotton fibers and makes the thread rather wiry. In a strength test, it beats a comparable size poly, rayon, and metallic every time. In a heavily used quilt, this stiff, wiry cotton thread could do more damage than a soft polyester thread. And it is 100% cotton.
The point is this: The traditions, myths, and rumors that polyester thread will tear the quilt are not true. Under extreme use, a strong polyester thread might, but so will a strong, glazed cotton thread.