I have to disagree with this. Some mATX boards are very nicely laid out and provide an ample amount of breathing room for all the components. I built a friend's computer using the MSI 890GXM-G65 (http://www.newegg.com/Product/Produc...-269-_-Product) with an HD 6850 and everything had some good breathing room. I would guess that some mATX boards are cramped, however the ones I've had experience with are not.
I guess it's all just preference, though.