This is currently the only way that bbPress gives new users passwords. It serves a double purpose. The first is a record of a password for a user if they don’t end up changing it and second of all, it makes sure that people register with an actual email address (which stops most spam bots right there) because they have to retrieve their password from email.
If you need something, I would assume it would require a core hack unless someone can develop a plugin. Right now, I don’t think anything is in the works.