I think The Wedding Singer was the first show to actively market the idea of a post-show wedding proposal. From a marketing and revenue standpoint, it makes business sense to market this, although I don't know how special it is when it's being marketed like that.
I don't think there's anything wrong with a couple taking up the production's offer, as long as it's relatively short. I happened to be in the audience at a post-Wedding Singer proposal, and it didn't take any longer than a BCEFA fundraising speech does. The couple also seemed very nice (of course, who can really tell from something like that).
"What was the name of that cheese that I like?"
"you can't run away forever...but there's nothing wrong with getting a good head start"
"well I hope and I pray, that maybe someday, you'll walk in the room with my heart"