I disagree. A lot of recent software is stupidly resource hungry and workflows have changed to require it. A lot of webpages demand frankly insane amounts of resources to display, and some very popular ones (eg. Facebook) are major culprits so there is no getting away from it without banning web browsing.
A old system good enough for typing up reports is going to be seen to be inadequate the second someone sends something to it in a new format or the second someone sends an amusing cat video. Telling the user that it's good enough for work purposes and they should ask for things in an old format and tell their friends to stop sending the amusing cat videos tends to put you in Bastard Operator From Hell territory or Dilbert's denier of information services. Memory, low end systems that can take a decent amount of memory and a modern OS is so cheap now that it looks insulting if you deny them something as good as the home computer they got for a low price three years ago. If they've used a decent system they probably are used to leaving programs open so they'll bring XP to it's knees if they don't learn to only have one thing running at a time. XP isn't designed to be used like a workstation, it's a toy to run one game at a time full screen with a side benefit of being able to run a word processor so you can bring the games machine into an office.
Windows hit the maturity point with XP and now there is no reason to ever change
It's got that step backwards into a low memory ceiling which is now a very major reason to change for anyone that likes to have more than one window open at a time.
I do not know of any use a typical office worker could not do on a Windows 3.11 486
Put even simple images in a document and such a system is unusable - I know that from plenty of frustrating experience back in the day.
But HR does not utilize 4 cpu cores
If they want to burn a CDROM they need at least two unless they just want to stare at the screen until it is finished. I've still got a single core machine around that proves that point from time to time, although now it's just doing good duty as an X terminal for a guy who does all his real work on a cluster so the single core and low memory does not matter.
Now while I have some XP systems for users that don't need anything else, or on hardware that can't cope with anything newer (Dell laptop with a 1600x1200 screen and can't justify $5k to get something newer with as good a screen), it appears to me that the average user is getting up to stuff that needs more memory than XP can provide.
Also your HR strawman would be on Facebook most of the time and sharing silly cat videos a lot of the rest of the time so needs a powerful PC even if it is not for work purposes :) While they probably could do their work related tasks with "ed" on a dumb terminal connected to Xenix running on a 286 the workflow would annoy the crap out of them - the same with a less extreme suggestion of yours that they would consider as antiquated as my Xenix example. Giving a new employee a slow XP box is a way to get rid of them even if the older employees like XP.