I've removed quite a few inactive players from my team and the way I see it, if you join a team, you should be prepared to contribute and work together with your team-mates. What's the point of being in a team if you're not prepared to be a team player?
One thing that most team leaders end up learning (on this site, or in the real world) is that peoples' free will will never cease.
Expecting a ton of participation out of team members on a site with no real obligation may be fruitless if that's what you're going for. In my opinion, Wes' option is likely the best one, though it'll never guarantee that anyone invited in won't just log out for a while and be inactive.
You're always going to have, as you call it, 'dead wood' unless you continuously remove and admit new people. Of course, then it's a revolving door.