There are a lot reasons to want portraiture at your wedding. Images where people are not being directed by the photographer are essential; They tell a story and they narrate the Wedding, but we want images of our friends and families looking at us as they do when they're with us. That's the simplest reason.
Just having images of everyone looking at each other doesn't replace this. Another reason portraiture is important is that life moves fast.
How often will all of your friends be able to get together like this? What will this be worth in 10 years? What about the guys? How often to they put on a "Tux"?
If you're going to wear a Tux, you might want to try to pose for a Photo. Come to think of it, If you're going to marry a handsome guy or a beautiful girl, you might want a dreamy fine art black & white portrait that you happen to be in.
You might also like to thank everyone by sending them a photo of yourselves gazing at them as though you're with them.