Is there a difference between a benediction and a blessing? Not an etymological one, at least.
I don't believe that's correct. According to the Online Etymology Dictionary, benediction is (clearly) Latin, whereas blessing is old English. The hypothetically pre-Christian, proto-Germanic *blodison is about marking with blood, whereas benedicere/eulogein have far more secular and far less messy readings. Unfortunately 'eulogy' has non-marriage-friendly connotations.
Of course I didn't know all that when I suggested benediction. My original theory was that blessing has more religious connotations than benediction.
Recently, LWers Will Ryan and Divia Melwani (now Will and Divia Eden) were married, with Eliezer Yudkowsky officiating.
I've been to 40+ weddings in my lifetime, and this was my favorite ceremony yet. Here is the video, and below is the transcript of Eliezer's... what's it called? "Blessing"?