I was reading a forum, I think here, where it stated because of 16:10 vs 16:09 aspects, it still cuts some off the sides when that black bar and bottom and top scale happens on the monitor. Something to do with the slope of the diagonal has to be adjusted too so you still lose some left and right even with the black bars on bottom and top. Some people argued but the person presented the math behind it and the other agreed and understood his point.
Anyone know how the math works behind that or if that (you still lose some horizontal view when scaled to 16:09 on a 16:10) is correct?
I guess my best argument is you simply tell the 1920x1200 monitor to blank 120 of the horizontal lines so that the remaining 1080 lines are illuminated. Thus you will have 1920x1080 pixel illuminated, and 60 of the top bars will be black, along with 60 of the bottom bars.
I fail to comprehend how a 1920x1080 in letterbox could be different mathematically from a 1920x1080 native, because it's the same pixels? However, I'm assuming your video driver is capable of doing this, or you are willing to edit your edid info so the monitor is indistinguishable electrically from a native 1080p? I recall using my Nvidia card to drive a monitor like this, I think it was a custom setup resolution for a 1600x1200 monitor to drive it at 1600x900, and it worked great with letterboxing.
Later on, with a 5870, I added the EDID information to allow me to run Starcraft 2 in full 16:9 wide aspect ratio (as you can see above, it is to your advantage to run 16:9 instead of 16:10). Before doing the EDID trick, Starcraft 2 wouldn't allow me to run the 1600x900 resolution, because my monitor did not natively/electrically identify itself as providing this option.
Anyway, that's my long-winded way of saying that it seems using 1920x1080 pixels would be the same no matter whether you have additional pixels available but darken them? Do you remember any more of the argument going the other way? Perhaps it was something about DPI or scaling? Note that I am anti-scaling in this presentation, I'm arguing for using letterboxing/black bars instead of distorting/stretching.