I don't know what RP is
Received Pronunciation is a UK term that largely replaced the term The Queen's English, and was originated I think at the BBC as a codified form of common communication.
Doesn't this get close to the common threads examined here - that there is no such thing as the right and wrong way of speaking or of expressing yourself in various written media? That rather, there is the appropriate and inappropriate.
Just as in modes of dress, most of us find little trouble in changing mode to suit the occasion. This rarely poses a comfort problem, until two separate worlds collide (and the family member hears the email laughter!).
Business communication demands brevity. Sharing a complex of thoughts, feelings and impressions with a friend suggests more languid and exploratory style (often involving discursive byways), and which may employ patterns of speech that rely on shared references, ambiguities, and half-formed thoughts about fishes...
And if everyone spoke in full sentences all the time, I would have been denied many a chuckle through the unconsious humour of elipsis (see Directions thread examples). I would regret that as much as I would regret the absence of the finely-turned and fully-formed sentences found in the prose of, say, Sebastian Faulkes.
