I think what's missing with email communications is the writer's ability to change gears a bit. The change of voice was almost automatic when writing a business letter--it was (is) serious work. That change from normal voice to business voice just hasn't evolved in the email process. Some do it, but for many, the two worlds have collided.
Perhaps I'm over-thinking it all a bit -- I'm for communicating and I care less about the rules than results. When receiving an email, I don't lament the sender's poor spelling or grammar, if I understand the message. Proper spelling and grammar make it easier of course.
When discussing this subject, I can't help but remember the Mad Max movie with the Aussie kids living out in the desert and creating a new language for themselves.
