Webers do not have any oil in them when new. And you can't season a porcelain enameled paint surface. You can (and will) always gunk it up with grease from cooking, but that's not seasoning per se, because nothing can ever get "into" the surface as with for example, cast iron.
With a new Weber, you could just as effectively give it a quick soapy rinse with the garden hose if concerned about factory dirt or germs. Of course, as you say, high heat from charcoal would also take care of that, too.
Sorry if that all comes across as pedantic.