I tend to agree with you (see my sister comment about regulators regulating) but it's worth noting that in this particular case the Justice Department did pursue the case but agreed to the most ridiculous settlement terms possible (the companies in question promised to follow the law for five years -- something they were already obligated to do.)

Edit: DOJ Press release http://www.justice.gov/opa/pr/2010/September/10-at-1076.html