From the New York Times:

The White House official who briefed reporters on the speech said Mr. Bush would take detailed positions on Social Security in coming weeks and months, but only to the extent that doing so would help Congress move forward. The official, who spoke before an auditorium full of journalists, insisted on not being quoted by name. Scott McClellan, the White House press secretary, said the goal in not allowing the use of the official's name was to keep the focus on Mr. Bush.

Can anyone imagine an auditorium full of webloggers, told not to quote a public official by name, being docile enough to honor the request like the Times, Washington Post, New Orleans Times-Picayune, Detroit Free Press, and many other papers?

Atrios identifies the official as White House Communications Director Dan Bartlett.