Sadly, as technology gets more and more "micro" and the number of different things our consoles are expected to do continues to increase, the overall lifespan of our consoles is going to keep getting shorter and shorter.
The smaller sizes of our microchips means that if there is a physical flaw or issue with the chip, there's a greater chance it will negatively impact the lifespan or performance of it. When you also have a bunch of different functions that a console is expected to do, there's more things that need to talk with each other in order for the system to work right.
Back in the NES days, you had a couple of controllers, an A/V out, and the game cartridge. That was basically it. There was no complex encryption schemes, no hard drive access/recognition, no networking, no high definition audio/video output, etc. etc. Things were a lot simpler and the technology behind it was fairly simple as well. As a result, the lifespan of those things is comparatively great compared to today.
Right now, our PS3 has to be able to handle the encryption/decryption of the games, audio, video, HDMI stuff, etc. etc. in order to run. It also has to be able to properly communicate with the network, and access the HDD. More tasks to accomplish means more hardware. More encryption/decryption needs means more complex setups where errors aren't tolerated. More work being done means more heat generated by the system and heat is a no-no for the lifespan of our consoles.
In addition, as consumers we want low prices. We don't want to pay through our noses in order to enjoy our consoles. The manufacturers, however, need to make money on the consoles they sell otherwise they will be in the red. To make them more reliable means more expensive manufacturing costs and either a lower profit margin for the company (bad for business), or higher cost for the consumer (bad for consumer). Therefore, companies look for the cheapest way to manufacture things and give them an "acceptable" lifespan.
Yeah, it sucks when our consoles die and I'm not trying to say that we should be happy with it and just carry on. I just think we should at least understand it and make our decisions and future expectations based on this. With console generations changing every 6 or 7 years, a lifespan of 5 years or so is acceptable to the manufacturers. They figure that if someone's console dies, they'll just buy the next generation.
I have two PS3s. One is a fat MGS4 40GB version that I thought was dying (turns out it was my Onkyo Receiver's HDMI4 port that bit the dust), and a slim that I picked up because it was cheap, I had funds I could spend, and figured it couldn't hurt. (Actually looking to sell the MGS4 one since I don't need it anymore, but since it's not Backwards Compatible and I wouldn't sell it with the game included, I doubt I could get anything for it. May just give it to my father so he can watch Blu-Ray movies with it). So I honestly haven't had any PS3 issues since getting my MGS4 One in November of 2008. Only have an issue with my Onkyo's HDMI board so I'm trying to save up to get a new receiver to have on hand if this one fully bites the dust. (Oddly, the only issue is with HDMI4 where the video signal craps out but the audio works fine).