They can take the biscuit because they know people will still buy them, it makes perfect sense from a business view.
It doesn't. Volume with less profit per item makes the most business sense.
This is why Titan is priced so high, because they know only
certain types of people will buy it. It's not meant to be a volume part, and I don't think they've sold particularly well as gaming cards, but rather as a viable alternative for people who want K20X performance for significantly less money.
You can't really blame nVidia for the 7990's price either, that was AMD's choice, and whilst its price to performance ratio isn't anywhere near as bad as the Titan's, it's still not great. Granted you do get a load of games with it as well, but for the kind of price they're asking there really should be 6GB per GPU RAM and the cards clocked to at least 1050Mhz.
But anyone interested in 7990 performance has the option to pick up other 7990s for pretty much twice the price of a 7970 anyway.
Those 7990s occupy the area that the GTX690, whilst the price of the 690 isn't great, it's at least understandable in regards to the prices of 2x GTX680s, so they're not charging a silly money "premium" over two single cards.
These high end cards from both AMD and nVidia aren't really intended to represent volume parts though, they're the niche end, not to say that excuses or justifies the price, because it doesn't.
I don't consider these parts "enthusiast" parts either, which I've noticed a lot of people are using to justify the high prices. These are
not enthusiast parts, they never will be. These are "throwing money at stuff" parts, and that's fine for those who want them, it's their money but let's not try to pretend they're high prices because it's enthusiast parts.
Enthusiast parts are parts that are generally high on the performance/value and overclock very well. That was generally the sort of product that kicked off the whole overclocking thing in the way it went off in the late 90s. Now the word enthusiast has just been misappropriated by people who feel they need to justify the silly prices that they are willing to throw at getting more FPS than anyone else, whilst also saying they don't feel that they should have to justify anything.