I think you struck on an important point. For clients Wordpress is a godsend. If you quit contracting or the client needs to change developers for one of a thousand reasons there's a massive pool of talent that can step right in and make adjustments. I've taken over Wordpress sites and the learning curve is almost flat (save a few weird plugins). Anyways, it's a whole lot better of a situation for clients, developers and productivity in general than the days when everyone had a custom framework that solved the same basic CMS issue.

Is there another CMS that has the same featureset and the same extensibility? I've tried a few, but keep coming back to Wordpress, even though it is annoying and a resource hog. It's too easy to extend, and it has most of the stuff I need built in to the core (as of 3.0 at least). I wish there were an alternative platform that ran on Python and Sqlite with the same polish in terms of features and ease-of-use, but I haven't found one yet (correct me if I'm wrong!)

Yeah, been working with it for quiet some time on and off and still regularly need to search to find out where a function may be being called from.