Was talking to MIL yesterday and she said she has been to 3 where this has happened.
One was a classic jilt - the bride didn't turn up, the other two there were issues at the ceremony. Fight between bride and groom at one ceremony and bride leaving another ceremony.
Seriously - 3??? 
Although she did say in her lifetime she has been to well over 100 weddings (receptions, she has been to less ceremonies)
It got me thinking that it can't be that uncommon?
Has anyone been to a wedding where this has happened?