I don't see that at all if I'm honest. Every day there are threads full of helpful advice. It's perfectly natural once the question has been answered that users start to wander and go off topic, but that doesn't stop the next person jumping in and asking something else - or if it does then people apparently feel quite happy to start a new topic and get a lot of advice and help very quickly. I think we're much better at that than Talkbass.
Typically it can be hard for long term users to see this as they become so familiar with the members and ways of the site that to them it looks like nothing is new and that things should be in a WIKI or some such (a typical response on TB is 'use the search function') but a revolving door or Q+A is the lifeblood of a forum and I'm very pleased with how welcoming and friendly people are here. Mods don't need to step in because there's nothing to do, the place moderates itself (sometimes even in OT!)