You don't have to post the body of your fics directly to the community. You're welcome to use a fake cut, as long as the proper header information is included in your community post. However, while most people tend to crosspost their fics with a fake cut, you are not by any means required to post your fic (fake cut or no) to the community. You're welcome to simply post only at your own journal... It's just nice for people who are looking for something to read as they browse the community (likely getting you a few more comments, and maybe getting you recced in newsletters, since the quibbler_report usually pays a lot of attention to our community), and it also lets us mods know when you're finished, so that we can put up a congratulations post for you.

Hopefully that makes sense. I guess that's just a longwinded way of saying no, you don't have to. XD