Businesses exist for one reason...
Businesses exist to maximize their profit. Even when a new product comes out, I think it is rare that they would sell below their costs to garner public interest. Businesses try to capture the public's interest by advertising and, in this case, through the media. Besides, if they did sell below cost, they would eventually have to raise the MSRP quite a bit to start gaining a profit. This would surely upset consumers, who can easily look up what previous MSRP's are and why they would increase.
In the Prius' case, Toyota is (was) essentially a monopoly. Yes, there are other hybrids on the market, but the Insight is not really a direct competitor, and the Civic and Accord hybrids are not the same market-wise (much less MPG, higher price point for Accord, Civic not a direct competitor). As such, they were able to limit production and drive the price even higher than it would have sold for if there were more to sell. Now, with more competition coming and more marketing from Honda and others, they're more of a mix of an oligopoly and monopolistic competition. This means that they compete primarily though product differentiation (what makes one "more special" than the other) and not as much on price, but of course the price competition is still there (they are car manufacturers after all).
Moreover, Toyota has stated that they are indeed making a profit (see the previous posts here). My point is that if you think a business is selling something at a loss for an extended period of time, I've got a bridge to sell you.