Of course Apple wants to protect their revenue. But they focus their litigation efforts on companies that, in Apple's view, try to sell devices by making the look and feel imitate that of the ios. Microsoft also competes with the iPhone, but I doubt Apple will sue them as vigarous as Samsung, because Microsoft developed, again in Apple's view, an original take on the smartphone concept.

Or, possibly, they just focus on suing companies that are successfully competing with them?

By the way, I have no problem with Apple suing to defend the look and feel that characterize their brand. It's the obvious patents that worry me.

I think that is at the core of this issue: Apple feels Samsung copied the iPhone experience, without any effort or even vision on Samsung's side on how to create this experience. Blind copying so to say. So Apple wants to sue them on look and feel, but they can't; what I remember from the Microsoft-Apple litigation about look and feel is that it turned out that look and feel is almost impossible to patent and defend. That is my explanation on why Apple is now suing over their obvious patents, because they cannot sue over look and feel.