You realize I'm not asking "can Nvidia do those things". Nvidia had "Twinview(tm)" when I last used them which allowed multiple monitors and was compatible with Xinerama on an API level.
That just meant you could extend your desktop across two monitors and when you maximize something it only maximizes in the monitor it is displayed in. It doesn't stretch across the whole virtual desktop splitting itself between the two screens.
However.. since it was only an Nvidia proprietary thing which was emulating Xinerama that meant utilites meant for configuring Xinerama didn't work with Nvidia cards.
Here's why that matters.
If you were using for example KDE (and I am assuming Gnome was similar) you could go into the control panel and change how your multiple monitors are set up. You could switch between desktop stretching vs cloning. You could swap left/right, etc... It was very easy and tidy... very Windows like.
BUT if you had an Nvidia card.. nope! You still have those functions in your control panel... but... THEY DON'T WORK! Instead you had to load this proprietary Nvidia app which then makes edits to your xorg.conf for you. Then.. it would restart X! So... all your applications you had open... now are closed.
I just did a Google search for Nvidia and Xinerama. The first result was an Ubuntu page about using Twinview. I take that to mean that your "years and years" comment is wrong and you are just assuming everything is ok because yes.. you can have two monitors.
Two monitors? Hell, I've run 12 monitors on Linux using the NVidia drivers. You can edit the xorg.conf file yourself, also. You do have to restart X, though.