It depends how narrowly you define the market segment. For all phones you'd be right. For "full face capacitive touch-screen smart phones/computers" Android and iOS are the two leading contenders, with the places differing depending who you ask.
From his perspective all that matters is a phone that runs a decent browser, or has a decent screen and interface and can run an "app". Hence Android and iOS are the two big gorillas in the space.
My advice to him would be to just make a web application that works in enough mobile browsers and be done with it since it will work on all of the other platforms he's got listed as well as saving him any more work for iOS and Android.
I've been using Chrome for the last 2 months, and today was told Firefox wasn't working with a wordpress blog I have to administer... since when does firefox have problems viewing things? I thought that was IE's job.