XP works just fine on hardware that supports it. As for IE, they’re not obligated to make sure new versions work on 12-year-old OSes. Apple won’t even talk to you if you’re still running 10.4 (Tiger) which is only half as old as XP.
Try installing Apple’s 12 year old OS (OS X 10.1) on a new Mac. Let me know how that works out for you.
It will work as well, so long as you use it on the same PC from 1999. It may or may not work on a brand-new PC if the hardware manufacturers don’t write drivers for XP.
But IE 7 and 8 did highly improve on their predecessors. The jump from IE6 to IE7 is one of the most revolutionary things of the last 10 years in the web dev world. You might not see that as an end user, but it allowed a better product - a website - to be delivered to you.
You also realize that the computer industry has advanced much, much more rapidly than any other business in the history of Earth right? That comparison isn’t apples to apples or even apples to oranges, it’s apples to motherfucking alien zygotes from the planet Xenobulus IV.