Thank you. I was coming to that conclusion, but that doesn't seem to be a complete answer.
File /etc/rc.d/xdm has this line:
command="/usr/X11R7/bin/${name}"
Apparently the directory in that and other files should be changed to "/usr/pkg/lib/xorg", but the "xdm" package I installed with pkgin doesn't modify or replace that file. It seems like it MUST be changed to get the modular version of xdm (/usr/pkg/bin/xdm) started at boot instead of the base version (/usr/X11R7/bin/xdm).
When I installed NetBSD, I selected a full installation from the menu instead of full minus X. So now how can I remove the base X files? A four-year old
wiki page says to execute "pkg_delete -r x11-links", but that command returns:
pkg_delete: No matching package for basename `x11-links' of `x11-links'
I'm fumbling my way though the pkg_ commands looking for a way to show what the basename for X is and how I can uninstall it. I'm thinking of wiping the disk and reinstalling with the minus-X option, but that's time consuming with no guarantee it will work.
BTW, I like the "pkgin" command and the pre-compiled packages. But there remains a confusing mishmash of base and pkgsrc commands that are non-obviously orthogonal or mutually exclusive or redundant.