Yes, you're entirely right -- this is weird and kind of contradictory and
it's hard to figure out just what this was supposed to mean. What I
spelled out is what we arrived at in previous discussion, but there may be
other possible interpretations. But it's hard to figure out a way to use
/srv by default in packages and not end up tromping on whatever structure
the administrator sets up there, and a lot of sites use /srv in various
internal ways.
One interpretation that people have taken in some packages is to require
that any path in /srv be configurable with debconf via package
installation, but that's a little dubious since prompting should be
avoided wherever possible, and not everyone's comfortable with it.
Other distributions that I'm aware of all use /var the same way that
Debian does: as the default location for all data for packages. So just
avoiding using /srv seems to be the consensus interpretation, even though
the words aren't particularly clear.