Agreed, though one can be aware of a busy thinking mind also but it is harder and when one is there is a sense of silence that is somehow bigger and deeper than all the chatter, which is what I assume you are referring to. Why? I would would have said it naturally converges on whatever is appropriate to be aware of at the time. If at the time one is practising anapanasati then yes, if practising a different technique then maybe not, if eating lunch or walking or doing any number of other activities then awareness should converge of the activity at hand not on the in & out breathing specifically. The breathing in & out is a preliminary sign of being alive, placing ones awareness on breathing in & out is a very good way of developing the minds capacity to be aware, probably the best way to start for beginners, but it's not the only way. Understanding the difference between the process of breathing and the process of awareness that monitors breathing among other things doesn't consititute alienation, it sows a deeper understanding of the mind-body processes. In my experience giving all importance to one meditation technique is a good recipe for getting into a rut with it.