c.i., there's definitely a host of circumstances in which "common law" isn't equivalent to a "real" marriage. I'd have to look up specifics, though -- let me know if you want 'em.
patiodog, yeah, if you get right down to it, marriage is a pretty odd institution. It was mainly about property rights, including the wife as property, for a long time. (Again, have to look this up -- did a bunch of reading around when I got married and did a lot of "but where's the
romance???"-type exclaiming.) If you go waaaaaaaaaaaaaaay back, like cavemen (-women, -people), it's probably about kids and preserving genes and that kind of thing. But a lot of the modern institution of marriage has to do with "yo, papa, you don't own her anymore -- I do! Give her away already."
(Is anyone surprised that there was no mention of "obey" in my marriage vows?
)