well when it comes to extended warranties on custom, or "boutique" systems, you really don't need more than three.. i mean, people who buy these things want to them so that they can brag and all that, but in three years? you can easily buy a system for a quarter of the price and probably get more performance. So, there's no use for more than three years warranty because many of those people would have already updated those pcs (the insides, like mobo, cpu, gpu, ram, etc..), or the ones with deep wallets would have bought newer ones...
Also, there are many people who like pcs, new technologies, games, and so on but don't know how or don't have the guts to build and overclock their own machines.. well, it's probably the overclocking part that weighs down on most people, so they'd rather opt to buy a machine built by.... experts.... who overclock it for them, at a nice premium.. if you can afford it, why not? not many people complain at the price of a Mercedes S 65 AMG now do they?