While in some ways I agree that these password rules enforcements are not ideal (they are hardly scientific, they seem much more "common sense" to me), I think

While in some ways I agree that these password rules enforcements are not ideal (they are hardly scientific, they seem much more "common sense" to me), I think making you use a harder-to-remember password is part of the point. The current received wisdom on passwords is that if it's easy to remember, it's easy to guess. That said, I'm not crazy about the inherent paternalism of this sort of thing. I think allowing weak passwords with a warning is, in most instances (not including corporate IT and situations where you're requiring that the user protect your private information rather than their own), a preferred way to go. Informing people when they are making a weak password should at the very least let them make a choice about how much they care about their own security.