2 questions about EXPIRE setting in gnus

[winsphinX]

i set 'total expired' in gnus mail, and the mails are
disappeared after 7 days, I saw only about ten mails in
group buffer, obviously many mails were expiresd,but in
mini-buffer, it was still shown 'default 400', why? and the
disappeared mails are deleted or are only invisible?

and the second question is, when i set the same setting in
gnus newsgroup, is doesn't work. i need such a result -- the
news before 7 days will be automatic deleted to free my disk
space.