Android's much more fragmented and yet hasn't had any trouble making gains. As much as Apple and Apple-boosters have made of fragmentation as some great cost, actual market experience hasn't really born that out in terms of selling handsets.
It does make things more difficult for developers, sure.
Not only it is implied apps should develop a specific layout just for it, but IIRC it also has a different viewport size which is not a multiple.
On top of that, the 6 already reports a new viewport width in the browser, which I guess it can't be helped though.