I think this is an issue endemic in tech and not just in email communications. In a previous role I used to meet a lot of startups, very few of them could articulate what they did and why it was valuable to me or my customers. I'd hoped that the rise of unconferences and the move to Ted type presentations might have started improving communication in our industry, but it's change is slow in coming. Perhaps it comes down to the fact that we don't teach engineers to communicate, don't reinforce good/poor examples at work and then wonder why people aren't great at it.