Understanding Diagnostic Port

So I understand modern cars have these diagnostic port, u plug in a gadget, BAM! tells you what's going on.

Question#1: Is this standard for all cars/brands, I mean is, one tool suffice for my Honda as well as my Mercedes?

Question#2: For street-Joe, knows enough cars to be dangerous, how about a cable to my iPhone and the App got all the smarts to explain all the archaic diagnostic codes am looking at?

Can it be this easy?