That's fair. I didn't bother with the rumble version since none of the games I was buying a controller for had a rumble feature (DDO, SNES and NES ROMs).
After some testing, it seems that the connection where the cord meets the controller gets loosened inside or something--maybe worn out from extended use/movement--and causes the connection to the computer to drop as you move your hands.
When I posted here even small movements were causing problems. For the time being (until I can afford a new controller), I've looped the cord around the center of the controller twice. This takes the pressure off of the joining point and acts as a pretty substantial buffer. It works, but makes reaching across to the Start and Select keys a little cumbersome and reduces the amount of distance I can pull the controller back to me, so I find myself sitting up more often than reclining (though that may also be an indicator that I need a new glasses prescription as well).