I must say that this is a cultural change for the government. For some agencies and some departments it's been a difficult decision to put out raw data. The desire is to make it as clean as possible, to massage it, instead of the intention being to get it out there, let people use it, and see what they can do with it. That's been a tension that has existed in the creation of data.gov.
On March 2nd, 2011. See this statement in context.