Why manipulate immigration numbers in the first place?

Mike Munger at Kids Prefer Cheese and Greg Weeks at Two Weeks Notice have commented on a recent WaPo story on the Obama administration's manipulation of immigration numbers.  It looks like the administration implemented a host of accounting gimmicks to ensure that last fiscal year's deportation numbers exceeded the previous one.

But in reaching 392,862 deportations, U.S. Immigration and Customs Enforcement included more than 19,000 immigrants who had exited the previous fiscal year, according to agency statistics. ICE also ran a Mexican repatriation program five weeks longer than ever before, allowing the agency to count at least 6,500 exits that, without the program, would normally have been tallied by the U.S. Border Patrol.

I don't really understand why the administration is trying so hard to make it look like it deported more illegal immigrants in fiscal year 2010 than it did in fiscal year 2009 (each ends September 30).  Well, I do understand, but if the administration wanted to be honest present a perfectly reasonable explanation for why 2010's deportation numbers were down from 2009, it could just have said that as a result of increased deportations during Obama's first year in office (as well as increased deportations during the Bush administration), a slower U.S. economy, and stricter border enforcement, there are fewer illegal immigrants living in the United States.

The estimated number of illegal immigrants living in the United States fell from 11.6 million in 2008 to 11.1 million in 2009 (Pew Hispanic Center estimates).    As the total number of illegal immigrants living in the US declines, we are also likely to see fewer people deported.

Just take a page from the drug war playbook and say that fewer deportations is a sign of success.  The when the number of illegal immigrants in the country increases (again) and a greater number of people are deported (again), you can call that success.