[jmulder]

But that's not the point. The point is to have easy to understand cues for the receiver on how important the message is, with the sole goal not to disturb them for messages that do not require immediate attention.

A phone call can always be followed by a confirmation e-mail explaining it again for archiving purposes, but it is incredibly selfish of a sender to assume that the receiver will immediately read and act on the e-mail he receives. Most of us just get too many e-mails to assume every e-mail is important -- it's usually the complete opposite anyway.