I just ate a store bought roti (a flat Indian bread, like a tortilla) and baking powder is a listed ingredient. Why does a flat bread need baking powder? There are no bubbles to grow, are there?
The baking powder does very little to the roti. If you are making them to eat as soon as they are done, there is no need for baking powder. I assume you are asking about Indian-style chapatis, which are flat breads with no yeast leavening, very similar to flour tortillas.
There are many publications that have studied the effects of chemical leavening agents on wheat Mexican tortillas (which are similar or even identical to chapatis). They all find that the thickness of the bread changes by about 5%, not worth it in my opinion.
For a fluffier tortilla, more critical than the baking powder is, when cooking, to get both surfaces done and dry as fast as possible, so that they may act as a barrier to the steam that develops inside. In commercial settings this is achieved by hot-pressing the dough. Commercial chapatis and tortillas manufacturers have to fight staling–the drying and toughening–and I imagine that every little improvement counts.
Rotis made at home don't have baking powder. I am sure the store bought ones use it to make the rotis extra soft and fluffy it is heats up.