I haven't seen the examples yet, but what I've understood, and maybe a "simple point of view" of what I think it is, let's clarify you something.
When you develope an android app, you have to deal with Activity_Start, layouts changing on rotate, Activity_Pause, Activity_Resume on start and then everytime you change from one Activity to another.
Sometimes you don't know if develope your app in a single activity, loading differents layouts, or create several activities and go and return from one to another.
B4XPages is a way of create an app in a single activity, making easier to load diferents layout, and not having to deal with pauses, resumes, etc...
Maybe I'm wrong and when someone corrects me, make it clearer to you.