My Appologies for laughing, but the thought of ever going back to a PHPBB community based forum makes me want to laugh.
When BBF just started out (as BlackBerryClub.com) it was a phpBB driven community, up until the instability and server overload features of phpBB were revealed. See this archive for yourself: http://web.archive.org/web/200502030...rryforums.com/
phpBB is a free, open source software, with many security issues and constant patches necassary, it barely supported this community when there was 6,000 or so members, and had the server do some crazy things such as 30 minute SQL queries.
Therefore, the decision to switch to VBulletin was made, which is a paid board software, takes up similar server resources as a 60,000+ userbase board, as phpBB did with a 6,000 users.
In terms of the other points you mentioned,
Signatures (picture signature that you find "cool") have been disabled on this site to reduce page load and clutter.
Avatars, as long as within size limits are not limited by board software, but rather by the users creativity.
In terms of a Richer feel, Im not sure about that one.. Styles and the way a site looks and feels is dependant on the template, therefore dependant on the owner. This site is feature and stability rich as it needs to support a large community. The days of adding flash to every page just to make it look cool are over. This site is succesful because it follows a similar style model RIM does: Simple and Effective.