I have a really nice app to read them called Media Player Classic -- I just don't have an app to manage them. Writing apps to manage every single file type I have is very inefficient compared to using a general purpose file manager. You abstract out often-used code rather than copy-pasting it all over the place, don't you?

The only way to advance the state of the art is to let go of a lot of the notions of what we think a computer should be.

The fundamental definition/theorem/axiom/whatever of computer science is the Church-Turing thesis. We haven't come up with a practical notion of computability more general than that, so it is by default the state of the art. Following from that, I think a computer should be a real-life manifestation of a universal Turing machine -- something that can run anything computable (taking into account resource bounds but also providing all the resources it can) without being beholden to another entity. Anything less is an appliance, a toy, and is not fit to be called a computer.