Signature apps are what makes platforms. For an odd and interesting example, look up 'Torque App' - I wont provide a link as I'm not involved or any sort of freelance marketer - basically its an app that allows an Android smartphone or tablet to directly interact (via a US$10 bluetooth OBD2 adapter) with the ECUs of a running vehicle, allowing dynamic logging of hundreds of variables, live display of most of them, changing of vehicle settings on the fly, resetting of glitching systems, reading and clearing error codes, optimisation of fuel economy....
In the performance and economy/environmental motoring worlds as well as the home-based car repair fraternity this app has such a following it influences phone handset or tablet choice among whole forums. iPhone doesnt have a comparable app - well there's one but it requires a particular adapter that costs a lot, and doesnt do as much. Windows store also has a few apps but none of the have the following or the universal recognition, and some are reported as having problems with bluetooth adapters.
For me, what Windows store needs is the sorts of apps that are making waves already on mobile devices,not bastardised versions of Windows desktop apps. It may be too late.