Application.isMobile() equivalent of Application.isWebPlayer() ?

Is there a isMobile() equivalent of isWebPlayer() for telling when the app is being run on a mobile device?

No, and I don't think isWebPlayer would have existed, had OTEE been more ambitious from the start. Application.platform will tell you what you need.

You can add it if you like.

function isMobile() {
  if (Application.platform == RuntimePlatform.IPhonePlayer ||
      Application.platform == RuntimePlatform.Android)
    return true;
    return false;

The docs show you how to differentiate between all the platforms. Handy for debugging since you can toggle debug messages on when running in the editor only and output them to a debug log file for builds.