Primarily because of Middleman's local data[1]. Basically any .json or .yaml files located in your Middleman project's /data dir are exposed via the data method as a big iterative array.
This makes it perfect for polling an API during build for whatever data you need, then tossing the whole .json ball into the /data dir for exposure.
Don't get me wrong, I love me some Jekyll, but I find Middleman covers pretty much all my bases these days.
Close. Siteleaf/Prismic is an either or deal. Siteleaf is much simpler architecturally, and works for like 80% of my clients. You basically get page collections and optional meta data.
Prismic is much more blown out - I bring it in as the big guns if I need to support a more complex hierarchy or need specific document masks/permission levels/etc.
The deploy via Heroku is neat because it does a git clone of the repo on github before running the Middleman build (therefore consuming the API), so all I have to do is push my changes up to Github and they'll get picked up on the next pass (sometime in the next 10 minutes).
It's just real fun to work with, with very few failure points. After all, the worst thing that happens is the build fails and they get served a 10 minute old static site.
Did they miss the old WP text editor or are happy with the new CMS?
My only take on this setup is the perceived or apparent fragmentation since the resources are scattered over many places and not on a single point like in a typical WP installation, what do you think?