Why can't my Mac do printer sharing with my iPhone?

If I enable printer sharing in my preferences on my Mac, my other Macs can see it, and can print from it. Why can't my iPhone 4? I don't care if I can print directly to a wifi printer as long as I can enable Printer Sharing and have it work with my iPhone. Am I missing something? Why can't I print using a shared printer on my wifi network?

And where is siri for the Mac and Apple TV?