Re: >something to tell the grandchildren (Dr Mouse)
I was about to reply with something very similar. Themed weddings are not a new thing, and marriage itself has been around since LONG before people were believing in most of the "traditional" religions. If this couple have found a way to celebrate their relationship that both of them enjoy, then I feel it doesn't affect their chances of staying together one iota.
As for the assertion in the original post that non-religious families tend to also be non-traditional in the family sense, I know a number of completely non-religious families as well as religious ones and don't really see any correlation between the two things so I'm interested whether it's a "fact" or just an assumption.
The last sentence in your post really says it all for me - "What matter is not what you believe, but how you treat others". I couldn't agree more - regardless of what choice of religion (or not) people have made.