Can some OBD II Scanners detect more problems than others?

To put it more simply, the $50.00 code will read all the codes that your engine may store. It probably will not read code from the anti-lock brake system or the supplemental restraint system (air bags). Since you already know the code it's throwing for the torque converter you can just read and erase it if you choose. If it shows any other code, you'll have to look into it further.