The only specifications that are known that Expresso and CELL share is the fact that they both use Power Cores, and even That is not exact(Expresso has 3 Power cores to the PS3's 1).
Similarly Cell's only relation to POWER is the fact that it also utilizes a power core. After that they fly two entirely different roads.
Cell= General Power core+ Streamlined Co-processing elements. Not anywhere in the same league structure or function(not power, power is different) wise to Expresso.
CPU longevity has little to do with the progression of GPU power. PC's would be outright unsustainable as a platform if you needed to go out to spend $200+ on a new CPU every 1-2 years. They need to make sure their parts play nice. Moore's law still exists and happens, however it will not discount youth parts.
If you bought a nehalem processor at launch, chances are it lasted you into the age of Sandy Bridge(about 3 or so years)(at the very least), the same way that if you bought a Sandy Bridge Processor at launch it will most likely last you until Haswell next year(or even past that). You wouldn't say that GPU's haven't significantly changed between 2010-2012 because of that.
Graphics while a common feature of advances are not the only one. We have increases in scale, AI, particle effects, advanced geometry ect....
We have benchmarks, specifications and examples. Which is why I'm entirely baffled by a claim that GPU's were roughly the same over a period of 4 years during which games like:
Far Cry 2
were All released. They all look nothing like each other.
Battlefield 2142 was resource heavy, and took a multiplayer and combat arena scale to a different level.
Crysis won over everything due to the magnitude of employed physics, detail and overall scale.
Fear 2 concentrated efforts on particle effects and surrounding details.
Far Cry 2 was detailed open world.
Stalker was large, lush, detailed(granted buggy as well), and had some of the most perplexing adaptive AI known to games. NPC's would actually work, hunt, kill, defend and move around the place, making them frustrating to find(as they would get bored).
Honestly, I don't know where that statement is coming from, but it's downright false.
Edit: Not leaving out ARMA....Absolutely ridiculous game technical wise in terms of size and physics.
1,2,3,4. The whole can benefit