Nigel is dead on about one of the main differences between written and spoken messages.
A way to make a point about the differences between between verbal and electronic messages is part of an excercise from Interpersonal Communications.
" I Didn't Tell John You Were Stupid".
If you place the major emphasis on each word, one at a time as you read the sentence, you create a completely different message at each pass.
The emphasis on "I" implies someone else did...
The emphasis on "Tell" means I implied..
And so on...
There is also such an immediate quality in electronic communications that a lot of people (including me) don't spend a lot of time creating the message.
We all mean well...we just need to consider the impact and clarity of our messages.
Russ