(disregarding sammyF70's joke about tablet fanboys)
You know, there are people out there who just do not need a keyboard. The keyboard is optimized to construct words in an alphabetic language. Chinese users have struggled since the beginning of computing to figure out a good method to construct words on the keyboard. The most optimal solution now is a combination of some typing shorthand + auto-completion. Chinese is a language best written by hand. For that, a touch interface is actually superior.
The only good point you've made is the elimination of one of the dimensions of movement. However, the combination of piece value and target file is much more significant than a 10% compression of the game. For example, at any given point in the game, there's very few different moves possible from those conditions. The non-moving pieces are non-moving; even in chess notation nobody cares about those.
Additionally, the goal of this exercise is to deterministically convert chess to music. So I think you're missing the point if you count that as a negative.
Calling this 20% of music is a bit harsh as well. True, many elements of music are not represented here, but arguably this is adding an additional element.
Living on Earth may be expensive, but it includes an annual free trip around the Sun.