The dishonorable discharge part is due to the fact that if you were given a dishonorable discharge, they feel you were likely found guilty of a crime serious enough to be a felony. Maybe, maybe not.
The domestic abuse part is because they figure if you beat your spouse you'll eventually escalate to killing your spouse. Maybe, maybe not, but quite likely in many cases.
I find both to be somewhat reasonable, despite the fact that I fall under the classification of "gun nut" around here. Yeah, I suppose you can make the case that a misdemeanor is not a felony, and a dishonorable discharge could come as a penalty for a misdemeanor.