How many mobile phone web browsers support javascript?
If most mobile browsers' support for javascript is limited or nonexistent, then it makes sense to optimize for Safari, since iPhone users will be the only ones able to use it anyway.
They should be optimizing for Safari but making it work in all other web browsers. The whole point of using/making web apps is that they work on more than one platform and in more than one browser. I can't see a damned thing because I use Firefox.
If most mobile browsers' support for javascript is limited or nonexistent, then it makes sense to optimize for Safari, since iPhone users will be the only ones able to use it anyway.