OK, so I wasn't totally off-track thinking "the wife" is not the ideal term. It's like there's "the plumber", "the realtor", "the vet", I just don't think "wife" fits with that category. In defense of my fellow men, they probably don't mean anything derogatory or negative, it's just words. As Christine said earlier, maybe they just picked it up from a tv show or a buddy.
BTW, I know a guy who referred to his wife as "the warden." I thought it was kinda funny, but he was just kidding. A spin-off of "ball & chain."
ETA: I see Wishingonastar was ahead of me on "the dog"