Actually, those guys make only a tiny slice of the value per click. Banner advertising is a low return game.

Now...if you control the landing page and conversion funnel, basically delivering paid customers (vs. clicks) to a paying merchant, your value per visit goes up by a factor of 10 - 50. $.25/click vs. $10 - $30 (varies by product).

Now imagine a company that launches dozens of offers with hundreds of variations and plows it's bankroll back into the best (most profitable) version (for years at a time).

Yeah, $400MM is possible.