Actually, I use a brillo pad to wash my car so there usually isn't any need to scrub. But just in case of stubborn tar spots, I use a wire brush designed to clean grills. If that doesn't work, I'll use my own mixture of paint thinner and gasoline and a blow torch to burn it off. Then I take my car for the ol' around the block quick dry, but I live on a dirt road in florida where it rains everyday, but I haven't had any problems with the mud before. When I'm ready to wax, I apply it with a high speed, rotary sander. I'll let it sit for about a week or so just to make sure it really cures. Then, I use the brilo pad again to take it off (it did such a great job the first time!!).
But I could be wrong, because it's not your way and we all know that you have muuuuuch more experience than I do. Which is understandable, because you've been detailing since you were a kid. It's only common sense that someone who has been detailing the same car every week for the past 21 years would know way more than someone detailing thirty different cars a day for the past four years.
Now if I could just be a d**k for a second... Since you're so picky about choice of words, such as wax pad and applicator pad, you should know that washing DOESN'T remove all surface contaminants. Baked in pollen, brake dust, tar, tree sap, etc... are all surface contaminants that aren't removed during washing. Other, harsher processes are needed for those "contaminants". And as I previously stated, if you wash your car properly, every part of the car should be as clean as the rest so there's no need to worry starting top to bottom. I don't know how the weather is in Washington, but dirt doesn't pour from the sky in a matter of minutes here in Florida. If it does there, maybe you should contact the EPA. And assuming conditions are as bad as you say they are, your microscopic dust, pollen, and fall out will simply settle after you've applied the wax and will be rubbed all over your car when you remove it (not to mention the dust created from your wax).
So, don't talk to me about killer dust that's gonna ruin your wax job, because it won't. You're not gonna convince me that in the three minutes it would take to wax from the bottom of the door to the roof, would make any different than if it were done the opposite way. I've already stated that there are several ways to do this. It's just that my way is far superior in that it saves time and doesn't over complicate things and has the same desired effect.