[Boboff]

First wife, Diamond Solitaire... Lasted 12 months.
Second Wife, Elizabeth Duke been 12 years.

Marriage is important if you are bringing up children together, but not fundamental. It does make finances easier in the event of Death though.

[MK Chris]

Marriage is important if you are bringing up children together

The only reason I can think of is to stop the 'why do you have a different surname to your mum / dad' questions when they get to school age. That's getting more common anyway though.

[Nicola_Red]

Can I just stress that I wasn't suggesting the success or failure of a marriage rests on the cost of the rings!