That is a great machine and yes the cams are what does the decorative stitches. One cam can do several different type of stitches depending on the type selected. I have a 500A and although I have not yet played with it yet I am very impressed with all of its features.
That machine will do anything you want it to do and would be perfect for quilting!!
Maybe after I get finished doing my 128 I will get working on the 500A
Billy