Av gas uses lead because the engines for planes are still old school carbed. Also pump gas containing ethanol is a bad thing, very bad thing to have in an airplane where temps are below freezing since ethanol absorbs water, which can cause line and carb freezing. You can also adjust the mixture manually on planes, run them lean to extend range, so the lead helps with lean running. The lead acts as an octane boost, the higher the octane level, the higher the compression can be before detonation(pre-ignition) occurs, which when running lean in the airplanes is needed.
You dont need high octane in our small gas engines, the compression is not very high, but you should run at least 87 octane, 90 is better as it give a smoother running motor when leaned out. Running 100LL really is not needed, though the engines will run fine, just make sure you check the plug every so often as it will foul it up from the lead. Also, be VERY careful handling 100LL, as lead can be absorbed through your skin and lungs. Lead is nasty stuff if too much gets into your bloodstream, causes nerve damage and affects your brain. If you set up the plane fuel system properly, drain the tank before storage, run the carb dry and keep it sealed up, the odors are minimal, you will smell a little on the plane, but for the most part that will go away after a day or so. I have my T-Clips with the FG-11 in my basement, and other than a couple drops of exhaust oil that dripped, there is no odor present. My DLE20 powered 4*120 also has no fuel odor, but my big DA100 powered Extra 330L I left fuel in it, so my trailer now reeks of fuel. I need to find a better line setup so I can drain it without having to pull the cowl, or flip it upside down.