If it allows me the same benefits as the language does on the web then I'll be using it, regardless of how many people think that makes me "not smart".
That was part of the OP's point. "PHP's killer app is the LAMP stack and $5 hosting."
That option makes PHP useful in many cases where arguably better languages would not be smart choice.
But, without that same value in the mobile space, what's the case for using PHP over, say, Objective C or JavaScript or Ruby or Lua, other than not knowing Objective C or JavaScript or Ruby or Lua?