The prevailing theory seems to be "copyright infringement" as this comes on the heels of Joe Biden's announcement of Operation "In Our Sites" (great pun, roll eyes) which seeks to protect the interests of the Obama administration's arguably greatest political benefactor, the entertainment industry, through rigorous enforcement of copyright law.
Others argue the response was uncharacteristic for DMCA maneuvers and therefore must mean the FBI suspected one (1) or more (2–72,999?) of the 73,000 hosted blogs to contain child pornography and/or a threat to fatherland security. Still others believe this is merely a breaching experiment, a practice run, to guesstimate how adversely the public would react to something more consequential.
QUOTE(Helium.com)
BurstNet has reportedly refused to allow the owner [of blogetery.com] access to data from the site, crippling his capacity to bring the site back on a different Web site provider.
Dump your databases. Dump them often.
Some coverage:
*http://www.helium.com/items/1893892-why-73000-wordpress-blogs-were-shut-down-by-the-us-government
*http://www.geek.com/articles/news/73000-wordpress-blogs-shut-down-by-u-s-government-20100716/
*http://www.infowars.com/feds-ignore-due-process-first-amendment-shut-down-thousands-of-blogs/