Same torch, different gas. Mapp burns hotter. Does that matter when lighting charcoal? Not really. It does make a difference when plumbing however. The faster you can make a joint hot, the less heat transfers to another section of pipe or fitting. Heck, I've gone to soldering with MAPP/OYX for a really hot flame.
For lighting the WSM I go with one or two of the weber cubes on the side.