My personal opinion in marriage, is that it's made to make the wife the happy, it's their dream to get married since the day they were born (unless they are the new age kind of women). Some gay couples might look into it for a form of security, or some sort of statement. I would understand if they would want to get married for a economical stability such as taxes and health insurance benefits. But the government does not support some of this actions, so some benefit such joint taxes are not yet attainable.
Overall I find the marriage issue to be joke, how many couples are getting married and then get a divorce months after, it's like a fashion statement to get a divorce now days.
You can find unmarried couples that have more stability in their relationship, than any married couple will ever attain, it's all about communication.
Then comes religion, but thats another issue.