Why?

...do people make announcements that they're going to make an announcement. As much as I like Fred Thompson, I think this is just silly:
WASHINGTON (CNN) – Former U.S. Sen. Fred Thompson will officially announce his candidacy for president on the Web next Thursday, September 6, sources working on the actor's formal entry into the race told CNN Thursday.

Now Fred isn't the only person guilty of this, they did it on "The View" and the Spice Girls reunion tour dates, and plenty of other instances. I think it's just dumb and redundant. The end.