Sorry, the center channel was INTENDED in the 5.1 specification for dialog. It doesn't mean it is always used correctly.
My understanding is that the center channel is intended for whatever sound is meant to be localized near the center, no matter what kind of sound it is.
Please clarify which "5.1 specification" you're referring to. The standard for 5.1 broadcast is ITU-R BS.775 which as far as I can tell does not mention anything about the center channel being "intended" for dialog.