Read the GPL carefully. In addition to the one in it, you
are supposed to put in another
warranty. IANAL, but I suspect that if you didn't someone
could come up to you and say, Well by section 5 I decided
that I didn't want to accept your stupid terms, including
your lousy disclaimer, and so I am suing you within an
inch of your miserable existence!
I don't know whether this was possible, but the FSF
certainly thought there was some issue or they wouldn't
have put in those instructions...