Tesla has a fairly small # of customers compared to the phone market overall. Each of the smaller phone OSes has millions of customers.. The distributions may be different (maybe 90% of tesla customers are iOS?, no one knows), would be nice for tesla to go by its customers (which right now leans more towards early adopters, etc which is going to knew the numbers a lot)
They could have a browser app and get near 100% coverage, or go by actual data by surveying actual people with cars (maybe by what phone types are paired with the car via Bluetooth).
I'm not sure internet traffic is accurate, tablets skew that number, and you have to be careful about US vs worldwide (things like Norway where there are a very large number of S reservations, also has something like 10% WinPhone -- there may be important markets that will lead them to want to support all of them).
or they could make some API public and the community will fill in the gaps. (I will try my best to get an app for my phone)