Soldato
Civil marriages in their present form have been going for decades, the idea of a civil marriage has been going for centuries (probably thousands of years in fact). Think of common law marriages if nothing else e.g. married by habit and repute - no religious ceremony (not even a ceremony at all) yet you can have all the legal rights if it is believed you were/are a married couple.
Marriage just opens up a whole new selection of legal rights, you can do the same with a civil partnership if you wish. A will is not an adequate substitute really as it isn't designed to do the same thing.
http://en.wikipedia.org/wiki/Civil_marriage
Common Law Marriage isnt legal