It's simple really, when you stop to think about it.
While none of what you say is incorrect (this time), the analysis is way off. Like I said before, it's only Microsoft that is too lazy to spend the time really tuning the code in their OS. Linux does it, the *BSD people do it, Apple does it as well. While a P4 will be a P4 forever, and won't be able to compete with a Core i3/5/7/9 which are 3 generations beyond the P4, not to mention several design factors of the P4 lead to it's rather lackluster performance, there IS something to be said for making the most of what you have.
You see this a lot in the video game world, specifically with consoles. As time progresses, developers learn to better squeeze every last bit of performance out of a system's hardware. The hardware itself has never changed, it's just a matter of learning how to use it more efficiently.
I have done some development work myself, so I'm not totally unsympathetic to Microsoft's position. Performance tuning is slow, tedious, expensive, and often times the performance payout is pretty low. It does have some positive elements however. It often forces you to streamline your code, which makes it easier to maintain later, and it also increases the odds of finding a bug that would have gone unnoticed otherwise. You also have to really think about the structure of your program and how to implement it. That generally leads to a much better overall program that is easier to maintain in the long run.
However, there does come a point where it really is pointless to try and support certain things. Microsoft is wrestling with that very issue right now with Windows, and that's why you hear about other operating systems Microsoft has in the works that aren't based on Windows. Sooner or later, pretty much every program reaches a point where it needs to go in directions you never anticipated at the outset, and trying to shoehorn in some of these features just isn't practical.
The catch here, is that NONE of this really factors in to your wildly inaccurate analysis based on the facts at hand.
A P4 w/ 1GB of RAM will never be able to match the performance of a Core i3 with 4GB, this is true. However, is it so unreasonable to expect that a new OS utilize a system's hardware to the best of its abilities, given the obvious limitations?
Next time, you might want to follow a thought through to completion before calling others stupid. You're the one making an argument on a flawed premise, that stems from an incomplete analysis of the situational factors. It's not a pissing contest about which system will run faster, it's about making the best use of what you have. Because not everyone can afford to spend $500-$1,000 dollars on a new system every time Microsoft comes out with a new version of Windows, and if you load Linux onto a P4 with 1GB of RAM, you can still get a couple years of useful life out of the thing as a desktop, and several more after that as a file server or something similar. It's all about what the system is used for.
Now run along child, the grownups are trying to have a discussion.