While I didn't make the suggestion initially, I can see where it may have come from and might be able to expand on it some.
couchdb has a concept called couchapp (think rails for webapps written in javascript) which allows the entire application from data storage on the filesystem to presentation in the browser to only require the couchdb process and the web browser. The data is automatically ready for bidirectional (or multidirectional) replication anywhere from offline apps to cloud hosting providers -- all active.
It purports to do for your web application what git did for your application development -- you can clone just the app from one DB to another, or clone the entire DB for backups, offline work, or even peer-to-peer production hosting or web.
I haven't done web apps very much myself in a couple of years, but that's one area that's a bit tempting for me since the ones I have been interested in have peer-to-peer data accumulation and offline work + synchronization needs.
* They all require two servers running (redis + a web server)
* None provides a framework for building an application.
* None provides n-way replication.
* None provides offline support.
I get that they do mean you can build a web app. The question above was why it would make sense to use couch instead of redis. The primary answer is because the database already does most of what you want (including serving the HTML to the web browser) since it speaks the same language as the eventual client.
>They all require two servers running (redis + a web server)
So? separating web service access to the datastore is simply separation of concerns and just good modular design. A redis hybrid solution is still going to be faster than Couch.
>None provides a framework for building an application.
There is lua scripting available in some of them and the application fx is generally on the client.
>None provides n-way replication.
Out-of-the-box Redis supports trivial (as many as slaves as you want) replication.
IMHO Redis comp-sci data structures provide elegant and fast solutions to the requirements of a StackOverflow Q&A site.