You and me both 

Sort of but not really.  It's a TN.  On the plus side no blotching, stuck pixels, dead pixels, and it has good clarity.  On the downside, mainly, it has a "brightness gradient" from top to bottom that simply can't be adjusted out - if you go through the Windows calibration you'll get it adjusted in the middle, but the top will be about 20% too dark and the bottom will be about 20% too light.

Odds are he's not even doing something where he'd be auto-correcting like that.  Only someone like a photographer would routinely have such issues on account of knowing to start with what everything was supposed to look color wise.

It probably is the PWM.  I've got a 2560x1440 Acer K272HUL that I picked up for under three that has no PWM dimming and it's much more comfortable to look at than the PWM dimmed laptop screen next to it, despite the screen being it's equal. My primary at home is a Samsung SA850 with PWM, but it's fast enough that it doesn't bug me much.  Some people actually get severe migraines and other neurological impacts from high frequency stuff, and even a good PWM controlled monitor with several hundred cycles per second at a low brightness is still just more of a problem for them.

Another thing to consider is motion blur.  My parents have a fairly high end Samsung television with the clear motion crap, and my eyes are fast enough that I see every little bit of distortion as it's doing the between frame fakes.  I can give myself a rather impressive headache in not a particularly long time.  If your TN panel has a lower latency it might give you more grief because of that too.

The last thing I'd look at is anti-glare, some of these screens add a huge amount of complexity to the image you're seeing by having a highly detailed surface to cut down on glare.  If you're seeing that on top of the picture, it can greatly increase the eye strain over a smoother display.

Thanks for interesting comments.

I think PWM is a big part of the problem because my eyes seemed to get worse when I lowered the brightness. The PWM fix is normally to raise brightness on the monitor to 100 % and then lower brightness in your graphics control panel. I haven't tried this yet.

I also think IPS panels are problematic for me. I experience them as more vivid than reality. I don't think reality is as colorful as IPS screens. Reality has some "greyness" to it (just like TN panels). I would like to call IPS screens "supernatural". This is of course highly subjective. I don't know what actual measurements say.

One would imagine that it would become easier to buy tech products as technology progresses, but this isn't necessarily true. I am not a big fan of 16:9 aspect ratio for computers either. IPS/LED in 16:9 format seems to be the norm these days.