I think all the unfinished games are definitely a part of the whole 7drl jam. Some individuals might hold off registering, and only announcing in they feel content with the result. But I'm also sure many people (myself included) enjoy the scattered devlogs and such that abound during the week. Even if you don't follow the jam so closely, you can always pick up which games got some interesting attention, good reviews, etc. afterwards. And some of the failures can really be as interesting as some of the successes.
As always,
Minotauros