None seem to have gotten it down yet.
Basically I agree. Content management is a lot less solved then spreadsheets or word processing.
Depending on the group of people using the installation I think this is huge. For user groups that include a big slice of non-technical people web interfaces still have a ways to go.
Lots of businesses have spent big rolls on CMS deployments only to continue farming out the maintenance of content to web techs because the interface "wasn't enough like Word."
Whichever companies develop platforms that Mom and Dad can use reliably will make a mint.
The obvious solution is to divide the software in two parts: a "framework" that takes care of storage, authentication, etc. and modules that implement features using the other part's API.