Brand advertising on the net is all about clickthroughs too, just like any other ad. That's why you never see a banner with no link. The brand advertising is Budweiser's website, not their tiny banner. Since clickthroughs are whats relevant, the same laws apply.
Eh, the click is there so they can measure it and get more transparency than a billboard. But even if you don't click on it, it's about as effective as a billboard - not useful for a specific sale but one more incremental bit of brand awareness.
That's wrong because it isn't the tiny banner ad that is the billboard, it's the website you get to when you click it. Budweiser doesn't sell beer on their home page, they advertise it.