Yup and this isn't even a question about marketshare. It's not like Bungie is some poor start-up in with limited resources, they're a big AAA game developer and they want their products to be on as many platforms as possible to please their entire fanbase. Building an app where the backend is already all done shouldn't be hard at all from my perspective as I develop for Windows and WP apps myself. Bungie should really get on building a Universal app if they haven't already.