Re: Oh joy!!
It's because the toy is popular, not because it is fit-for-purpose.
Obviously, if you add a keyboard and a mouse it gets closer to usable for laptop-type things.
This Office is supposed to make it usable without either. Perhaps it does, to a larger extent than the previous offerings anyway - Surface Office is properly usable only with keyboard/mouse, which happily come easily with the touch cover.
But, it is entirely possible to view and make (small) edits even just using my phone, any Office is better than no Office. Obviously other viewers must be able to do this because people send Word docs and Excel SSs all over the place but I feel happier sending the document on knowing it is not broken in some way.