On budget builds, or older machines, XP will always triumph 7. On newer high end hardware, that speed advantage has diminishing returns, because you simply wont notice the difference. The truth is though, the XP OS is still running faster, it's just that it's not perceptible any more.
He's talking about a new build, not legacy hardware. And since XP is legacy too, and as you say the speed difference isn't perceptable, there's no reason to limit yourself. Plus as I mentioned before, plenty of gaming benchmarks put Win7 ahead of XP in performance. If this is a gaming machine, you'll want to go where the highest FPS is. XP isn't it.
I'm sorry, but that's just incorrect. If anything benchmarks for DirectX 9.0c games are about the same if not higher on low-middle end machines using XP , due to less disk activity, less processes running, less memory consumption etc.
Again, talking about new hardware. An idle Windows 7 machine is just as idle as an XP machine. If the machine in question is underpowered, then yea XP will put it into the "sucks less" category. On current hardware, see one paragraph up.
Not quite turn of the century as you suggest is it now?
Read the article again. Released 2001. Service packs are just that, not a new OS but a collection of updates. And my turn-of-the-century comment was directed at the comment about Windows 3.1 anyway, which is well before turn-of-the-century.
If you measure "better" in terms of efficiency of resources, then yes it is.
How is XP more efficient? It's doing less things, has less capabilities, ergo less of footprint. Having a machine with a ton of memory doing absolutely nothing but looking pretty in a sysinfo report is hardly efficient. It's wasted resources.
All new games will first and foremost support XP and DirectX 9.0. Some may offer additional support for for higher versions, but developers go where the users are, and that's currently XP.
Since he's talking about building for the future, limiting himself to a legacy version of the DirectX platform is hardly smart. If you're planning ahead, the last thing you want to do is limit yourself to things that are already ancient history, or are quickly being shown the door. Both XP and DX9 are firmly in that category. Why go with the old version when you can get the latest, which just so happens to support that older one anyway?