I don't really have much experience with the British stuff. I must just watch the "normal" UK casting stuff.
A couple of things do come to mind.
What about animated shows? Many of them either don't list the cast (main or otherwise) at the beginning, or differentiate them at the end. For instance, Justice League Unlimited dumped everyone at the end. And it's debateable whether it had a "main cast" once it went the full Unlimited route. Kin Shriner as a "guest star" was probably in more episodes than Michael Rosenberg in those three seasons, or pretty close to it. Should animated shows be treated similarly?
Across the world, various countries and networks have different ways to list people. As noted with the ChrisAmon discussion, "Featuring" was big in the 80s. So is TVMaze going to add a different section for every different network/country that separate some cast from another for a reason? They separated "Co-Star" from "Featuring" for a reason, too.