Not sure; perhaps the controllers used in the Das, etc. are programmed to start up in Numlock mode, while others just fully reset on poweroff. You can fix this with a little utility called numlockx, probably available in your package manager. Just add numlockx & to your .xinitrc, or if you're using Gnome, add it to your startup session. KDE 3.5 has this functionality built in, not sure where it is or if KDE 4 has it.