How many startups out there don't have a clearly defined use case or have a use case that is precisely split evenly between desktop/iPhone/iPad/Andriod, and abs

How many startups out there don't have a clearly defined use case or have a use case that is precisely split evenly between desktop/iPhone/iPad/Andriod, and absolutely cannot get traction with out a tailored experience on each platform? I'd hazard a guess that the answer is none. It's not a big deal, if the primary users are desktops write for the web first. If the primary users are going to be mobile write for mobile first. If you have 'the best. idea. ever.' then you should have no problem securing the funding for a 3 person startup. Since you probably don't and are going to have to do a lot of iteration think about how your service is going to be used and pick the right platform first. Stop thinking about how to get your millionth customer and start thinking about how to get your first.