In any case, I fail to see how this is any more useful than Capistrano. Just being able to push arbitrary tree-ish hashes to a specific environment isn't very special, as that can arguably already be done with Capistrano.
The problem with capistrano is that it tries to abstract a bit too much of the underlying project and deployment environment away. minicap aims to fix that by providing a minimal, git-centric remote footprint. cap provides a great foundation, but makes a couple of mistakes in its recipes that are easily remedied with a minimalist approach like we've taken in minicap.
This also introduces perhaps a new workflow to many people, if you already work with Git. As you said, it isn't very special pushing any branch to any remote location. However, it has not yet been done by anyone else yet (from what I can see, I might be wrong).
For a lot of people, (again, not everyone), it is a joy to be able to spin up a VPS, being able to provision it with pre-configured settings and common dependencies with a few commands, and being able to have your application live in a matter of a few minutes without needing almost _any_ knowledge of Linux.
Of course it isn't for everyone and every project, but it's good (and simple) enough for me. Every project has different requirements for deployment and I sure appreciate the option to chose from a variety of tools.