The kernel is much more likely to be "actually" built from source by Gentoo users (in the sense of going and doing things with "make" in the kernel source direc

The kernel is much more likely to be "actually" built from source by Gentoo users (in the sense of going and doing things with "make" in the kernel source directory) than any other package. There are automatic options available for the kernel but the "just get the sources and handle the rest yourself" option is, I'm sure, more popular for the kernel than anything else.