kohlrak: When you see the format of the wallpapers and think of SVGs, you slowly realize t hat's probably precisely how they make them.
Darvond: You'd almost be right, but then there's the renders and clearly 3D objects in some of them.
3d is still 2D, in the end, unless it's stereoscopic.
But, anyway, i decided to grab 4 modernish games out of my inventory and look at their Wallpapers:
-Elminage Gothic: Character on background that could be cut without a second thought (especially from the left, since the logo isn't there).
-TW3 (8 wallpapers)1: Cutable background (rendered geralt, drawn background)
-TW3 2: Cutable background (rendered completely)
-TW3 3: Completely rendered, no background
-TW3 4: Completely drawn
-TW3 5: i'm really not sure, because it looks 3d, does not look drawn, yet that's one hell of a particle engine.
-TW3 6: Rendered (background is, too, with some sort of blurr filter which is what we see in the cutscenes)
-TW3 7: Drawn (creature looks rendered at first glance, but the lack of lighting effects [despite the shadows] suggest that it's drawn)
-TW3 8: Appears to me to be a 2d-render. The thing itself was probably just a texture onto a 3d model with only 1 poly and transparency, given the lighting effects seem fake and the lack of clipping (even though negative clipping is possible, no one does it). Smoke effect then comes from interaction and rendering near the flat model. Oddly enough, they actually cut the model out of the thinner resolution, instead of only the background, which is unusual, since it's the subject matter.
Arx fatalis (both): They have varying resolutions, but they're all completely drawn, and not generic. The way the clipping is done is precisely why they usually don't do wallpapers like this, anymore. The subject matter, although clearly cutable all the way around, is the most work, and it's getting cut from some of the wallpapers (which amounts to lost time, art, and money).
Aragami: Drawn (or at least appears to due to really well cell shading, but i'm pretty sure it's drawn). This is more like what you'll see, overall: You can add and cut away as much of that grey as you like to fit the wallpaper to your aspect ratio.