Yeah, BIAB is an extreme version of steeping, but more properly it is called mashing at that point. Instead of 1-2 pounds, you are doing more like 10!
I agree, the point of steeping grains in an extract batch is for flavor and color, not sugar (since the sugar is being handled by the extract). You do get a little bonus sugar from the steeping process if you do it right, but it is lower efficiency than a mash since it is usually a shorter time and less controlled.
In BIAB, there is no extract, so the grains play both roles, hence it is a true mash. BIAB is an awesome way to step into all grain brewing, as is partial mash a good way to start getting more of your fermentable sugars from grain.
About your beer recipe, I sometimes would steep dark grains for only 5 minutes (at the end of the steeping phase), to shoot for a smoother flavor profile. I am not an expert on dark beers though.