Not necessarily. They announced Sonic for Brawl quite late, and he drew in a lot of customers. They may be saving some big announcements for later.
They didn't put Sonic in until quite late. That's why a lot of Sonic's moveset is fairly simple and uses the ball graphic so much. Nintendo didn't have the rights to Sonic until closer to the release so they quickly added him in, it's also why we only see him at the very end of the Subspace Emissary.