My understanding of baking powder is that it supposed to be a chemical alternative to yeast, allowing a baker to leaven bread more cheaply and faster than yeast would do.
Is baking powder the primary method for leavening commercial breads that I would find in a grocery store like "Wonder Bread" and "Sunshine" and so on?
No way. I have 3 loaves of (different brands) commercial bread open at home now. None of them lists baking soda, baking powder, sodium bicarbonate or any other synonym I know of, and all three do list "yeast". In addition, Amazon website gives the ingredient list for the authentic "Wonder Bread classic white bread loaf", and it also calls out yeast, and not baking powder.
Quick breads made using baking powder are significantly different than breads or rolls made using yeast.
For quick breads like baking powder biscuits or Irish soda bread, regular flour is used and very little kneading is done - only enough to for the dough to hold together. Too much kneading or even mixing will make the bread tough since it will start developing the gluten.
In what most people consider bread, bread flour with a slightly higher gluten content is preferred and the dough needs to be well kneaded to develop the gluten. It's the stretched and worked gluten strands in the dough that provide the bread's elastic network holding the small bubbles of carbon dioxide released by the yeast. Bread made with baking powder has little give whereas bread made with yeast is 'springy'.
The two leavening agents are totally different with two totally different results and uses.
