SusanM -- No one is claiming that there is no commitment without marriage, the question is whether marriage is (or indicates) a "stronger" commitment.

Also, it is certainly the case that a married person may be less committed, even with the legal marriage, than another unmarried person (I bet that would be the case if you compared Britney Spears on her first wedding day vs. David Letterman, still unmarried).

But for any given person, the decision of *that* person to get married is an indication that *that* person is increasing his or her commitment level, and is in fact willing to make that legally binding. The fact that there is still the possiblity of escape does not mean that the relationship is not more binding than it was before marriage.