Companies spend a lot of money advertising because brands are valuable, and trademark basically protects brands. Branding makes goods less fungible, and is really the only reason companies like Prada or Ralph Lauren can sustain such high margins in what would otherwise be total commodity markets. When brands cease to have meaning to consumers, you end up with what you see in the PC industry: a race to the bottom that eats up all your margins.
Why does advertising support so much of the internet? It's a $500 billion industry world-wide, that's why. Without branding, protected by trademark, I think it would be a fraction of the size. And I don't think it would necessarily be a bad thing.