While you can silbraze with Mapp, you are limited on the size of tubing. I brazed up the lineset for my heatpump with silphos 15 and found that on a 7/8" fitting (3/4" in plumbing trade), a standard Mapp torch had a hard time getting the job done (especially at the service valves). On some of these joints, I found having the wife holding the propane torch while I hit it with the Mapp torch got the job done quickly and cleanly.
I know some HVAC guys will use a air-acetylene and others use oxy-acetylene. In the HVAC trade, it seems like Mapp isn't used much as these guys want to heat the joint fast (to protect service valves, reversing valves, etc.) and the acetylene torches are also able to get the job done if working on big chillers and refrigeration units.
A lot of it too is in the size of the torch (BTUs). The Mapp flame is hot enough, but may not have enough BTUs in your standard hand-held torch. Acetylene is used so much that you have a wide range of torch tips to choose from and can easily change out to get the right flame for the job.