sojrner :
While I see you have some good rebuild lingo, I still feel it is a bad analogy. Your analogy is more akin to having an 8800ultra on a $50 mobo with a low-end sempron and 512Mb ram. In that instance the 8800 is wasted and would never see it's full potential, just as your shorblock would never return the money spent on it with the rest of the engine stock...
No, the example you just presented is analogous to the 1000 horse power mustang stuck in first gear. It could perform much greater if it wasn't for the damn tranny (or in the computer case, the CPU and ram).
In my example, the short block will never increase performance by itself (I made no mention of increased stroke, bore, or compression for a reason), all it can do is support a high horsepower build. Same with a massive power supply. Let's say I put a 1000 watt PSU in my K6-2. It won't make the old computer any faster at all, but if I were to swap out the K6-2 setup for a Pentium D 840/8800 GTX kit, then that 1000 watt PSU comes in handy as it is easily capable of handled the increased load put upon it.
Your battery analogy is flawed. Computers don't just change power consumption. Parts will consume x amount of power in a range from idle to full load during operational state. That never changes. There is no "Winter" for a computer's PSU. Therefore, in your analogy, a 450 CCA battery will always be adequate for the vehicle it is in (as long as 450 CCA is the recommendation for the automobile in question), because the temperature never changes.
The only way to change power consumption is to change the components in the computer. Until the computers in the review are upgraded to power hungry components, a cheap, decent quality 300 watt PSU will serve them just fine. Or, in your analogy, a 450 CCA battery will work just fine starting up your 2.0L 4 cylinder engine, but when you decide to put in a 7.5L performance V8 engine with 14:1 compression, you'll definitely need a battery with more cranking amps.
Now, I could follow along with you in your analogy by insinuating that "winter" is analogous to a major hardware change that drastically increase power consumption, but this means to azzume (try spelling it correctly and see what happens) that an upgrade to power hungry components is inevitable, which is obviously not true. The computers could never be upgraded, or upgraded 3 years from now, and by then, we'd probably want to use a new PSU just to be compatible with new equipment (e.g, the 24 pin connecter, the addition of sata power connectors, and the multiple PCIe connections found on today's PSU that weren't found on PSUs 3-4 years ago). Or, these computers could be upgraded in a year or so, but with power efficient parts to increase performance without necessarily increasing power consumption. These are all possibilities that don't fit in your analogy.
sojrner :
A psu is the same way. The better efficiency and power factor correction can save a system on brown-outs and even mild power surges that a lesser psu would not. If you have especially bad wiring in your home it can actually burn out a psu... sooner on the cheap ones.
First of all, I argue that expecting a PSU to be your 1st line of defense in the case of dirty mains is a recipe for disaster. Why not use the equipment built for this kind of thing, such as line conditioners and surge protectors? The surge protection you get from an expensive, high quality PSUw/PFC is minimal compared to the same protection afforded by a cheap, decent quality psu w/o PFC. Most PSU can withstand a small surge, and a high quality unit with PFC isn't going to save you one bit when you get high by anything significant.