As with most things today, they have built in obsolescence however in the case of a computer, that can be anything from 1 to 3 months! Seriously, for the 'bleeding edge' stuff, the value starts to show up when the very latest version is released, all subsequent processors end up dropping rather quickly. You can also see this trend with the LCD Monitor. What used to be the 'in-thing' to simply be the first on your block to own an LCD monitor, the size of this has grown from 15" to pretty much 19" wide screen, to what I would consider the favorite 'size du jour' is the 22" LCD as it can be found for sometimes no more then about $50! So what's the deal with the Dual Core and the Quad Core? What should you be thinking about getting if you are thinking about getting something within the next month? Think about the bleeding edge stuff today as probably what you would be interested in within one to three months, is the way I see things. Therefore you shouldn't be looking back at where it has come from, but to where it is at the very forefront of technology and see how quickly that becomes 'old hat'. Plus, looking back on what you paid for something and what you can get it for today only depresses you anyway!
The following CPU ROAD MAP may help you understand just where we stand today.