As long as it's an honest, improve-yourself-or-I'll-leave ultimatum and not game-playing, then yes. Your initial description sounded more like a deception to me. (Probably because I've actually had women do that.) I suppose that "having the guts" sounds more romantic than "improving yourself."
If a relationship is important enough and you want someone badly enough, you'll do whatever is necessary, which often includes introspection and adjustment. Indeed, "Having the guts" sounds more romantic but it takes great courage to go after what, or whom, you really want.
On the other hand, how many relationships should have ended long ago, but dragged on because someone didn't have the guts to end it?
Guilty. I made a mistake in not ending my last relationship a few months earlier. My fault. It was clearly one-sided and I recognised it early on and thought maybe my intuition was off. It wasn't. I have a friend who has been with the same man, on and off, since she was 14. She's now in her early thirties and their relationship is abysmal - they put the "funk" in dysfunction. They've fought endlessly, had several separations, and even police intervention but neither will put their foot down and say "this isn't working". They're too afraid of being without each other even though they can't stand one another most days. Bizarre.