A supercar competes in a market; a hypercar doesn't.
The Ferrari 458 is a supercar. It is battling with the Lamorghini Gallardo, Aston DBS, McLaren MP4-12C and more not just for sales, but for more sales. The supercar is what makes money for exotic manufacturers, at least for the most part.
However, for many of these companies, a hypercar is probably a smart move business wise because it draws attention. You don't need to make that many of them (77, in the case of the Aston One-77, and even as low as 20 for Lamborghini's Reventon), but you do need to make the posters and get people talking.
People don't really walk into a Lamborghini dealership for the Gallardo - they walk in because the Murcielago, and the Diablo, Countach, and Miura before it, were so insane, so radical, and had such unbelievable visuals, that they have to have a Lamborghini. So they buy the Gallardo.
From what I've noticed, the supercars are, in most cases, the actual business part of an exotic company; priced competitively, with similar performance to its competitors. Hypercars are the price-no-object hype cars, made to draw attention to the brand so people will buy more supercars.
-Leadfoot