There's nothing of the sort to port your app. You can use 3rd party tools to create apps that work in both. That's what Titanium and PhoneGap were aiming at. With the new changes to the SDK Agreement, those look like they're not really "legal" or at least violate the agreement.
As for your other question, yes, people do create 2 separate apps. One for Android and one for iPhone. That's the way I currently do it and seems as if Facebook and others do the same.
