I've just come back to the KDE forum after being disappointed
with the numbers of post on comp.windows.x.kde (I prefer Usenet
to forums) and I've found that I can't see multiple post when reading
a thread.

Have I got a setting wrong (if so how do I fix that) or does everyone (with influence
in these matters) like the new way better?

You have the option to switch between the threaded mode and the linear mode. You are probably in the threaded mode. It's in the upper right, right below of the "answer" button.