Marriage vs Civil Union

Casey and I have been dialoging about same sex marriages at his place. It got me to wondering about the differences between civil unions and marriages. I found some interesting verbiage on it at the Fact Check website. Here are a few interesting excerpts from it:

We find three main differences between civil unions and marriage as it's traditionally viewed:

• The right to federal benefits. States that allow some type of same-sex union are able to grant only state rights. The Defense of Marriage Act passed in 1996 prohibits same-sex couples from receiving federal marriage rights and benefits.
  
• Portability. Because civil unions are not recognized by all states, such agreements are not always valid when couples cross state lines.
  
• Terminology. "Marriage" is a term that conveys societal and cultural meaning, important to both gay rights activists and those who don't believe gays should marry.

The Defense of Marriage Act (DOMA), signed into law by President Bill Clinton in 1996, stipulated that for all federal legal purposes “marriage” is a union between one man and one woman. Because of that legislation, all federal laws pertaining to married couples apply exclusively to opposite-sex couples.

The Government Accountability Office lists 1,138 federal laws that pertain to married couples. Many in that long list may be minor or only relevant to small groups of citizens. However, a number of provisions are key to what constitutes a marriage legally in the United States:

• Taxes. Couples in a civil union may file a joint state tax return, but they must file federal tax returns as single persons. This may be advantageous to some couples, not so for others. One advantage for married couples is the ability to transfer assets and wealth without incurring tax penalties. Partners in a civil union aren't permitted to do that, and thus may be liable for estate and gift taxes on such transfers.
  
• Health insurance. The state-federal divide is even more complicated in this arena. In the wake of the Massachusetts high court ruling, the group Gay & Lesbian Advocates & Defenders put together a guide to spousal health care benefits. GLAD’s document is Massachusetts-specific but provides insight into how health insurance laws would apply to those in a civil union in other states. In general, GLAD says, it comes down to what’s governed by state law and what’s subject to federal oversight. If a private employer’s health plans are subject to Massachusetts state insurance laws, benefits must be extended to a same-sex spouse. If the health plan is governed by federal law, the employer can choose whether or not to extend such benefits.
  
• Social Security survivor benefits. If a spouse or divorced spouse dies, the survivor may have a right to Social Security payments based on the earnings of the married couple, rather than only the survivor’s earnings. Same-sex couples are not eligible for such benefits.

Other federal areas in which couples in civil unions don't have the same rights as married couples include immigration (a partner who's a foreign national can't become an American by entering into a civil union with someone) and veterans' and military benefits (only opposite-sex spouses have a right to pensions, compensation for service-related deaths, medical care, housing and the right to burial in veterans’ cemeteries). Gay couples, however, may actually benefit when applying for programs such as Medicaid or government housing that require low-income eligibility. A spouse’s income is included in such applications, but a same-sex partner’s income is not. One change has been made in federal law: A provision in the Pension Protection Act of 2006 allows same-sex couples to transfer 401(k) and IRA earnings to partners without penalty.

So, I guess that the main difference between these two is very legal in nature and may not really mean much in the actual practice of living together as a couple.. with the exception of the perception of legitimacy. If a couple is legally recognized by the state (as civilly joined) then, from what I can see, the argument here is a legal one of federal proportions.

What do you think? Is the difference between marriage and civil unions mainly a legal one or is it more about being legitimate? Or am I missing something?