When a tow-bar is attached to the nosewheel of a 737 it is pretty much hidden from the flight crew. We are at the mercy of so many other people, trusting that they do their jobs correctly. I have to admit that I take the 'pin & wave-off' at face value without actually identifying the individual elements as they are moved away from the aircraft. It does seem pretty unlikely that the groundcrew would forget to remove the tow-bar after pushback.... but were they distracted by something at a critical moment?
When all is said and done I cannot imagine the feedback through the tiller is something you could possibly miss on taxy as the tow-bar jack-knifes and breaks off the engagement lugs.
RYR pilots always seem to be in a hurry.... Or is that my imagination?