Av gas is has a high octane, slightly more BTU per hour, and has less volitiles. It is more highly refined, however that has nothing to do with power. It is more refined to keep out both the lighter and heavier volitiles out. The lighter ones cause the fuel to boil at altitude and also promotes carb icing. The heavier ones promote sooting and thus can foul the plugs in those full rich take offs. If you ever see an STC'd airplane that runs on Mogas look at the exhaust stacks, there will be more soot in the pipe and the fuse around the exhaust. Since the fuel has less light volitiles, and less additives (other than the lead) it will store longer.

However, none of this helps small two stroke gas engines. The lead will foul the glow plug, and with the low compression ratio will not burn off and may even cause rings to stick. I once belonged to a full scale areoclub with about half dozen planes and they used the Avgas in their lawn mower. In a couple of years the valves stuck real bad, and even after that was fixed it had poor compression. I'm guessing stuck rings though I don't really know.