You might be surprised how many people would exclude languages like HTML on the basis that they don't describe computations. (I am more of a PL maximalist: any syntax that allows you to describe and manipulate some class of semantic objects in a machine-processable manner can reasonably be called a programming language.)
To me, the statement "just ... plain text" implies some level of simplicity that I don't see in the examples. It looks pretty complicated, in fact. There is no escaping essential complexity.
I took the like from the frontpage.
Maybe they want to attract non programmers and doesn't want to scare them with the word "programming"?