Because NetBSD already uses /boot for a different purpose, this version of GRUB has been compiled to look in /grub for its files (specifically, menu.lst and the loaders). If your root filesystem is of a type not supported directly by grub (eg, lfs), you may have difficulties. See the info docs for more details.

GRUB is not actually installed on your disk until you run a command such as grub-install /dev/wd0d or grub-install '(hd0)'