Why is From: limited?

I've got two questions regarding 5.4.6 From

1. Why is From: only a request header?  It would be nice to provide
   the address of the file owner so you know where to send comments
   if the author forgot to add a <LINK REV="made" HREF="mailto:...">

2. Why is it an addr-spec only instead of a full RFC822 mailbox?