You hit it on the head, Cloud. Also, a lot of drivers package a lot of extra apps along with the drivers. For instance a printer driver now magically comes with a demo of Pagemaker or somesuch crap. (And a photo editor, and rando other crap). A video driver now comes with a demo game or some smart overclocking software.
But to really hit it home check this one.
SetPoint is 50+ megs. A Mouse and keyboard driver.... I mean the mouse and keyboard already work without the extra driver! user input is generally interrupt driven, so you would think that the driver could fit in a 1mb file.