Straight French Couples Opt for Civil Union (not Marriage)

In France more and more heterosexual couples are signing a civil union pact of solidarity in lieu of getting hitched. The law was passed in 1999 to give gay couples a way to legalize their unions under French law, which will not allow them to marry. Now the ratio is 2:1, marriages to civil unions among heterosexuals in France. In 2008 there were 140,000 couples united by the pact, and 92% of them were hetero. The pact allows couples to file joint income tax returns like marriage, and are easily dissolved, unlike marriage.
( I wonder what would happen if there was such a law here in the states... )