"Later in 2011, the Census Bureau will release detailed tabulations from the 2010 Census, including counts from the relationship question," said a statement from the Commerce Department. "A footnote will indicate that there are no same-sex couples included in the husband/wife relationship category. At the same time, the Census Bureau will release counts from the relationship question, by state, that show the unedited data [that is, which do not recode same-sex couples who report themselves as husband/wife]."
This sort of thing is important - for a variety of reasons, it's in everyone's best interests to at least know how many same-sex married couples there are in the several states that have legalized it. They may not include those couples in the official count, but there is a large enough interest among certain social scientists, local and state policy-makers, and LGBT activists to have the most accurate count possible, which, really, only the Census has the ability to accomplish.
Waiting until 2020 just isn't an option considering how fast laws are changing in this area.