I'd been wondering about that, too. The thing is that less restrictive tickets give the traveller fewer rights under that condition.
Indeed, and for a more mainstream example than the Chathill one, what about the following -
The way condition 28.1 is written, someone holding an LM Advance from Crewe to London should reasonably be conveyed by any TOC, if the specified LM train was missed due to late connection, as the journey shown on the ticket cannot be completed. However, other than for the last train, someone using the outward portion of a LM Only Off Peak ticket (valid one day) would need to wait for the next LM service as the disruption has not prevented completion of the journey shown on their ticket whilst it remained valid.
Of course the condition in the, now superseded, NRCoC was very different, viz:
"If disruption caused by circumstances within the control of a Train Company or a Rail Service Company leaves you stranded before you have reached your destination printed on or stored on your ticket, and the Train Company whose trains you are entitled to use is unable to get you to that destination by other means, any Train Company which is in a position to help will, if it reasonably can, either arrange to get you to that destination, or provide overnight accommodation for you."
When ATOC (i) removed any mention of being stranded and (ii) replaced
" before you have reached your destination printed on or stored on your ticket" with
"completing the journey shown on your Ticket" (the key change being from "destination" to "journey") they presumably did so deliberately to widen the scope of the assistance to be provided. If that presumption is correct, the fact that the wording they used made things better for holders of a more restricted ticket than a less restricted one is down to poor drafting which could be easily rectified. In the meantime we can only go on Condition 28.1 as it is written.