Currently the x11-apps/xinit package depends on x11-wm/twm, x11-apps/xclock and x11-terms/xterm. Presumably this is because they're run from the default Xsession. However, it should not be compulsory to install those packages to get a working system; pretty much nobody is going to use Xsession or twm for anything serious, and many people will have some preference to xterm. I'm not sure what the cleanest solution would be - possibly the dependencies could be moved to xorg-x11 instead, so anyone emerging that would still have a working Xsession, but those that don't want the extra cruft could go with xorg-server instead.
*** This bug has been marked as a duplicate of 110880 ***