Interesting point but the bible does not (as far as I am aware) actually state what marriage is - i.e.what the ceremony should be, where it has to be, who can do it and so on. All we have is the intepretation of those who read the bible and interpret the scripture.

The only thing that determines what needs to be in a marriage is the law and while these differ in some fine details (i.e the English law states that a wedding can only take place in a registered building by a registrar and the building must be a complete building with walls and a roof while the American law is completely different and allows outdoor wedding) most of them say that all you really need to have in a ceremony are the bits where the registrar asks if any one objects and the 'do you' bits. Everything else is additional - put there for the benefit of those getting married or, if a religious wedding, the requirements of the religion.

It was also common in many periods of history for a couple who could not afford to move out of their parent's homes to get engaged but have a long engagement until they could afford to get married and move out. During this time they would live for all intents and purposes as a married couple, including sex. The betrothal agreement was taken as a binding contract and they had to remain faithful to each other as if they were married.

So, by not getting married in a church or even not getting married at all but merely making a lifelong and personal committment you are in fact as married in the eyes of god even if the law may have things to say about it (but that only affects your legal name, tax status, divorce rights... you know, unimportant things like that )

Just some interesting facts I thought may have some bearing...