Heh, by your argument a full fledged desktop OS doesn't need to support keyboards because hey, a lot of desktop systems don't have keyboards (touchscreen kioks), doesn't need to support sound (not everyone wants it), doesn't need to support mouse input, doesn't need to support ethernet, doesn't need to support displays (headless mode).
I mean, this line of reasoning is ridiculous. Proper full fledge OSes support the main use cases, not the lowest common denominator.