Ya, I mean it. The fact is that there isn't very much that the average person does with a computer that requires new hardware, let alone overclocking new hardware.
Windows has, with each iteration, become easier to use.
Drivers became more plug and play. Networks became self configuring culminating with Homegroup. New hardware no longer requires a restart or manual polling. Preinstalled driver libraries balloon in size exponentially. Ease of use and automation constantly improve and that takes up computational power, HDD space, and RAM.
Those nifty little automations and tasks can be easily disabled by the more experienced user, but why should they?
But that doesn't account for all of it, major increases in computation demands came from the software, not the OS itself.
Office programs get better and better at grammar checking, we are on the cusp of voice recognition being feasible (heavily CPU limited), people think their computer "froze up" whenever there is a slight delay and end up cutting power (causing OS file corruption or other issues).
Facial recognition software and voice recognition are here, but stand to benefit from faster hardware.
And games, games are very far from rendering holliwood quality cinematics in real time.
If you were to ask me what the primary benefit of using my desktop over my macbook Air is, I wouldn't say "the fast CPU" or "the fast video card". I would say "the 23" IPS LCD and bookshelf speakers". The fact is that even for me the power of my desktop is unnecessary, and I'm an enthusiast and my desktop isn't even that powerful. I don't mind making tradeoffs on my desktop to get largely unnecessary increases in performance. I have a good case with good fans and it stays nearly silent all the time regardless. Once you start having to power all this stuff with a battery though, you will quickly realize that you don't need nearly as much performance as you think you need.
I use an ultra portable 13" laptop that weighs 3.7 lbs... I certainly accept performance tradeoffs for better battery and lower weight, and for what I use it for that is acceptable... but there are many things I can do on my desktop that I simply CAN'T on my laptop... also, your Macbook air cost $1300... How much was the desktop?
And you expect me to believe that you play video games on your macbook air and that it is just as good as playing them a desktop?
As far as arrendale goes.. intel has a near monopoly... with AMD struggling intel has not been pushing anything noticeably faster. The need is there, but they are inching along in performance, while making headway in manufacturing cost reductions. (which somehow never get passed on to the consumer). Arrendale was about cutting production cost in half by eliminating the north-bridge (which also slightly decreased its size, weight, and power consumption)... And prices actually went up! GPUs, cell phone SIC, SSDs, displays, eReaders and other electronics where there is actual competition show tremendous growth rates. SSDs more than double in speed and size every year while going down in price by a 1/3rd or so... and its all useful. GPUs rapidly increase in performance, and its all used up to produce better visuals, etc.
The moment we see actual CPU performance increase it will be put to use, we already have uses for it, and there are more uses that people are not writing programs for because they realize they are not practical on current hardware.
Also, as I mentioned before... any pause long enough to be noticed (say, a few seconds) will send the user into panic and likely prompt them to damage their PC. Any of your non techy relatives MUST be equipped with the fastest PC you can manage to avoid that.