Why Are the Feds in the Marriage Business?

While watching an old episode of Kathy Griffin: My Life on the D-List on DVR, Mrs. Kid and I heard that there are over a thousand rights that gays are denied because they can't marry. Mrs. Kid mentioned (twice) that she was curious about what the thousand rights are, so I had to find the list.

A GAO memo to the Senate: Defense of Marriage Act: Update to Prior Report includes the entire list and this description:

... as of December 31, 2003, our research identified a total of 1,138 federal statutory provisions classified to the United States Code in which marital status is a factor in determining or receiving benefits, rights, and privileges.

So, my initial question was: Why are the feds so tied to marriage? Then I realized that they have no other option. If you want to tie a benefit, right, or privelege to people who are commited to each other in a real and legally-binding way, then the only way to do it in the U.S. is to tie it to marriage.

I want the U.S. federal and state governments to create and recognize civil unions. Without this, we'll keep on having these big problems with people denying rights to gays because they perceive that doing so would have religious implications.