There seems to be a bit of a trend of doing this at the moment.
If I were famous and a random invited me to their wedding I think I'd be a bit 'WTF?! Do you not have anything better to do/waste your money on than inviting me?' I just don't get it. I'm not one for signatures etc though - someone got my hat signed by Flintoff when I was watching England in SW a few years ago and as far as I'm concerned they've ruined my hat now!