Re: It was dail-up in more senses than the link....
"The original description of the system that I read used a telephone dial to interact with the system rather than a touch-tone keypad."
That's not possible. The breaks in the line that resulted would cause a modem to drop carrier. There would also be no facility for the * or # keys and there's no facility in a telephone exchange for those loop interruptions at the local exchange to be translated to something meaningful at the distant end - just noisy clicks over the carrier that serve no purpose. Loop disconnect signalling ceases to be useful once the distant line is answered.
Prestel didn't use MF4 signalling either - it wasn't possible to drive it from a phone. The MF4 signalling is inband and would have obscured the data carrier, causing a disconnect.