[vertex-four]

> And yet elsewhere, domain specific languages are preferred.

Yes, but that's because the DSLs actually provide something of value. Having umpteen different ways to store a list of values under a key, for example, doesn't solve anything.

> the domain specific stuff just moves into, for example, the key names

Anything that wants to manage the system already needs to know the key names, etc - implementing a single config file format is significantly reducing complexity because they no longer have to implement config file parsers/serialisers.

> I mainly use configuration management tools, like puppet, to keep a fleet of machines in a consistent state by putting fully formed files in place

These tools are currently primarily based on templating. If you ever have reason to write your own resources for them (if you have to edit a config file for something obscure or in-house), you're going to have to write a text-based template to convert from your nice Puppet data structure to the config file format - and probably get it wrong on edge cases.