Tunnels & Trolls has always had a pretty secure hold of the "solo play" corner of the RPG hobby. It really is what T&T is known for. The thing is, treating it as a solo only system, or a solo first system, really shrinks your pool of potential players (and customers).
It isn't just perception that T&T is aimed at solo play even though the rules are written with group play in mind. Look at the adventures published by Flying Buffalo. Dungeon of the Bear and Isle of Darksmoke are the only GM adventures I can think of off the top that FBI put out. The list of FBI solos is huge.
Mike Hill pretty much wrote about the same in the editorial of The Hobbit Hole issue #12: "... if T&T is to grow, writers should turn their attention from the potentially self-indulgent solo arena and back to the group." (thanks to the Trollgod for mailing it out so quickly)
Just think... if you want to play solo, computer games and console games are king, even for RPGs. Group play excels on the table top, whether it is real or virtual. Solo play with T&T is going to be targeting a smaller and smaller audience.
Fans of Tunnels & Trolls will be best served if writers would move from solos to GM / group play adventures. With many gamers dissatisfied with D&D 4e, now is a good time to present an alternative that is easier to learn and play.