In fact, despite the apparent bad press in some quarters and abject dismissal of this technique by some, the breath can be used as the primary object instead of the abdomen, albeit something not actively taught in this day and age.
If something is a concept and not reality - as Yuttadhammo asserts that the breath is -, the thinking that goes with that is that one cannot see the 3 characteristics of anicca, dukkha and anatta. And that means that anyone practising mindfulness on the breath cannot see the 3 characteristics and therefore experience insight knowledge. It therefore follows that one cannot achieve any of supramundane states (magga and phala) by practising mindfulness on the breath.
From my personal experience, I can tell you that the breath is rooted in reality and is not a concept; one can see the 3 characteristics when the suitable conditions arise.
I have enjoyed and rejoiced in the ongoing work by Bhikkhu Yuttadhammo in disseminating the Dhamma in the new media formats (youtube, facebook).
But now, seeing such a statement from him for those intent on meditation is not good at all.
reference: http://yuttadhammo.sirimangalo.org/arti ... questions/ (emphasis by me as seen below)
Why do we focus on the abdomen?
The abdomen is an obvious example of a physical phenomenon; it is the element of motion (vayo dhatu) as described in Buddhist texts. Whereas “mindfulness of breathing” (ānāpānasati) is technically considered tranquillity (samatha) meditation, “analysis of the elements” (catudhātuvavatthāna) is considered to be the basis of insight meditation. This is because, while the elements are experienced directly, the breath itself is a concept. For this reason, though watching the abdomen can be thought of as mindfulness of breathing in a way, it differs from watching in and out breathing in an important regard: the latter often leads to tranquillity rather than directly to insight into the nature of reality, while the former is set firmly in ultimate reality and thus conducive to insight into the nature of reality.