I think its the younger gamers of today who are never truely satisfied, they've been spoiled by either the PS2 or even the PS3 as their first console and thus taste of gaming. Where as the older guys (like myself) who grew up with Ataris, Amiga and megadrives still get that headshaking disbelief that we're playing games that look and feel like GT5 (and GT4 for that matter)
Ive seen it first hand when you put a truely awesome and insanely playable game from say the pre PS1 generation and its totally unplayable for them because... yes graphics and sound.
Bare in mind I'm only 30 years old so dont mean to sound like a 'back in my day' type of guy but I do seriously thing thats where most of the complaints are coming from.
Although I largely agree with your observation that the progress made on current console games still appears hugely impressive as an "older gamer" having experienced some of the stuff you mentioned I have to disagree with the misconception often found here that it's only the new "spoiled" (agree here although that's just jealousy
) generation who express discontent.
It's all a question of perception I guess, if you keep comparing current games to the ancient stuff we played as kids and always keep that frame of reference as your perspective than it's very easy to be satisfied.
It's healthy and amusing once in a while to look back to put things in context but not all of the time as then we wouldn't need progress in the first place.
Thing is, with every new hardware and therefore software development, the possibilities extend not just twice but multiple times (and in multiple ways) and therefore it's logical to expect more, get used to more and since you paid for a new generation of console "demand" more.
It's not just the games which progress, we (hopefully) do too, meaning that what was once perceived to be
the next big thing is now just an obsolete piece of junk you couldn't see yourself going back to.
I remember a story of an old car journalist who gave each new car he drove glowing reviews and praised almost each aspects whilst the same cars were often heavily criticized by other (younger and older) journalists.
Turned out the guy drove a 30 year old banger himself privately and only used that as his frame of reference as that's what he drove for years and years....
It's not a shame to be discontent if your expectations grew along with the new developments over the years (that happens all the time) as long as they're realistic, being pleased no matter what since the games of the past were so laughable in hindsight is not without risk either, it may seriously cloud your judgement too.
Stay with the program, no matter how old you are.
Whew, Im glad nobody knows my address. 
