Sorry Woodsy;
You simply can't compare a highway or road to a home driveway. Asphaltic concrete for a highway is a completely different mix and thickness than your home driveway, it is also under a totally different stress load than your driveway.
The reason they don't seal roadways besides the expense is traffic volume and truck weight would simply wear it off in short time and since most roads need to be repaved every so many years, it makes no sense whatsoever, which brings us back to
expense for no reason...
Your home driveway should last many more years than a roadway considering low traffic volume and no constant trucks with weight driving over it.
The idea of sealing it is two fold...#1 to protect moisture from entering through the porous surface and eventually destroying the gravel base or heaving during the winter months and #2 to protect the surface from harmful UV rays. UV rays pull the oils right out of the asphalt and make it brittle and crack.
Your analogy is like saying painting a wood house is not necessary after all look how long the old wooden Weirs boardwalk lasted....
Sorry but them's the facts!
Dan