When reading the first post, I had the same thoughts. I ended up thinking that maybe the things you had to do were the reason you couldn't attend, and was going to comment that it was a shame, since a convention on poly isn't quite the same if you can't go with your partners!
But it seems it's a different issue. Well polyamory is part of your life even if you are mono, because he isn't, so if you want to go to the convention, you shouldn't be shunned out of it. Even if he wants to attend on his own, you could always go to different panels or not sit next to each other.
I too believe the description meant that it was going to explain to people why the relationships were worth the trouble, and that it was why they wanted to talk to people who didn't already know why they were worth the trouble. I'm pretty sure they expect people in mono/poly relationships to show up, and I can't see them telling half the people to dump the other half.
I do agree that you should talk with him, ask if he wants to go on his own or not, and voice your concerns, saying you understand that they are not likely to happen but you can't help yourself from feeling that way. Hopefully he'll be able to address it, and if he isn't, hopefully after going to the convention he will know better!