I'm given it some thought, and I'm pretty sure that, for the wallpapers I offer on my comic's website, I probably don't *actually* need individual sizes for a given aspect ratio (4:3, 16:9, 16:10), and can likely just offer the highest-quality version and trust that most modern devices can (gasp!) scale bitmaps as need be. Shocking discovery, I know.
The vector season series, I think I'll still want to have raster versions, maybe in addition to actual SVGs.
The very tiny home of CaptainSpam and all the various goings on at Exclaim Industries (which is just CaptainSpam).