nnimap better than advertised

[Bruce Stephens <bruce+gnus@cenderis.demon.co.uk>]

The manual seems to suggest that deletion is a bit weird:

     Since the articles aren't really removed when we mark them with the
     `Deleted' flag we'll need a way to actually delete them.  Feel like
     running in circles yet?

     Traditionally, nnimap has removed all articles marked as `Deleted'
     when closing a mailbox but this is now configurable by this server
     variable.

But unless I'm missing something, the behavious is pretty much like
other mail backends: if I specify (auto-expire . t), and don't think
too much, things'll work just like they do with nnml.  i.e., when I
read mail (or delete with "d" or C-k or whatever), then the mail will
seem to disappear (but I can still see it in the normal way, by
entering the group with C-u <SPC> and things), and eventually, gnus
will expire it, and it'll really go (and be expunged).

Is my understanding correct?  If so, then this looks like it's exactly
what I'd expect based on my experiences of nnml (say), so why is the
manual warning me to expect something unexpected?