A lot of this is the result of the confusion in the community, there is the CouchDB Apache project, then the CouchBase work and their own "Single Server" releases that don't necessarily map 1:1 to the Apache versions. Then there is the CouchBase "Couch Server" offering which, from what little I can tell, is membase + CouchDB and their CouchDB build, according to their docs, isn't 100% 1:1 with the Apache CouchDB buil…
As you've noted, there's lots of implementations and variants, platform targets and hosted services. What ties them all together is that you can point your CouchDB client library (or curl! :-P) at any of them, and be off and running.
While having a tip of the spear with a consistent message, canonical implementation and download, etc. is one approach (and I could certainly live with better messaging from certain places!), I think people are convinced enough by the merits of the CouchDB model to effectively route around the lack of that and some have produced fantastic (compatible / interoperable) alternatives.
(FWIW, I've been using CouchDB for a long time with a lot of apps and instances, but have been able to use all of them with Cloudant instead.)
Insofar as MongoDB's fate is tied to 10gen's, the distributed nature of the CouchDB ecosystem is actually working out quite well AFAICT.