About the IRS case and the Defense of Marriage act that triggered Obama's decision.?

In this article, which IMO was poorly written, it says:

"Windsor received a $363,053 federal tax bill--a liability that she would not have faced had the federal government recognized their union."

Does anyone know more about this case? How could she get a tax bill that has something to do with her not being married to her lover? Even if she had drawn SS on the other woman's account, she was only married for 3 years, she couldn't have gotten that much money. I am wonder what all that money is about and how this applies to her not being legally married to this other woman?? I wish the author had been a bit more clear.

Here is the link to the whole article:

http://news.yahoo.com/s/yblog_thelookout/20110228/...