This is just a repeat of the xml database vs relational database debate. This fight has been fought so many times before - http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.113....
Xml database, key-value-store, relational databases, csv files, etc. are all ways of persisting.
These are very different disciplines with very different problems being solved.
The question in both cases is how should we model, query and update our data. The original tradeoff was that hierarchical databases and network databases were faster but relational databases were more flexible and maintainable (due to the separation of logical and physical data representation). Better implementations (eg http://en.wikipedia.org/wiki/IBM_System_R) narrowed the divide and made relational databases more attractive. Systems like Bloom (http://boom.cs.berkeley.edu/) and LogicBlox (http://www.infoq.com/presentations/wavefront) show that the same tipping point could be reached for programming languages.
So, ya, the question is "How do you pass information between sub-routines". Databases aren't expected to do much data manipulation between sub-routines. Programs are just wow so many ways to do it.
Thank you for taking the time to have this discussion.
Nitpicking now, but phrasing it that way supposes the existence of sub-routines. I would prefer to phrase as just thinking about control-flow and data-flow. Most programming languages have complex control-flow and constraint data-flow to follow along with control-flow. Most successful end-user languages have arbitrary but static data-flow and little to no control-flow.
> Thank you for taking the time to have this discussion.
If nothing else, I find that these sorts of discussions tend to be really useful to clarify my thinking and catch my mistakes. Civil disagreement is much more interesting than ideological agreement or disagreement :)