1) Different monitors have different native resolutions.
2) A lot are now even widescreen which have different proportions to more tradition resolutions.
3) Lots of people also requested a lower resolution, In fact more requested this than the resolution you are looking for.
4) The vast majority say the game plays fine on their flat screens, it apears to depend on the quality of the screen they own and the combination of what video card and driver they use.
5) It can be a big deal, but when Paradox offered a solution of a black border, people rejected that option so they got nothing.
EDIT: As for future support, the new engine is reported to be a fully 3D engine so this issue should not arise.