I really don't understand this either. I feel like once upon a time email clients used to go so far as to show you the full header by default; but UI trends mad

I really don't understand this either. I feel like once upon a time email clients used to go so far as to show you the full header by default; but UI trends made it important to hide anything too technical from the end user. It seems like a total dismissal of function for the sake of form. Especially since the uninterested just scroll a little to get past the techno-babble. I think having the header right there was good, it reminded people that email wasn't magic, there was understandable technology at work, and you could easily see what was going on if you cared to look.