Most video hardware drivers are built as modules, and most modules are available in a default install for the most common cards/chipsets (at least the open source versions). Problems arise when;
A) Hardware is too new for there to be available drivers (Like the newest NVidia cards & Intel HD 4200s, etc).
B) Developers allow regressions to creep in for a driver that have been fixed,
C) A user is trying to get display resolution on an unsupported screen geometry (like 1366x768 that many LCD TVs use), sometimes related to B, in that distros may drop automatic resolution setup support for a previously working chipset/display setup (Ubuntu 12.04, for example), and
D) Hardware that does not play nicely with standards Like EDID (again, TVs are a big culprit).
Kernel Devs get their drivers from the manufacturers or by reverse engineering the hardware. Most distros will carry those drivers that are not installed by default in their respective repositories. So, they're usually an apt-get or yum away, with maybe a little setup besides...
If you want to know what hardware is supported by default in a particular kernel, you have to have a look at. that kernel's kconfig file... But going about that, is not a topic for a thread like this... It would pretty much deserve it's own thread, distro specific.
Last edited by JaseP; 10-08-2012 at 04:55 PM.