Not really fair comparing a 15.x screenshot with no preview pane to a 16.x screenshot with one... ;-)
But more seriously, some users might want this feature:
as it protects your privacy by keeping senders (spammers) from knowing whether you've opened an email. Also, I suppose an an image could contain a virus or malware.
I like how some email systems work -- if the sender is in your Contacts (trusted), the image loads. Otherwise, you're prompted.