DCR, those letters are form letters that White House staffers write. They send them out to a facility that has a George W. Bush autograph machine to sign the letter. This is what staffers do mostly, just respond to the thousands of letters they get each week. They have form letters for every issue imaginable, both pro and con, and it's what they call "constituent service" so voters feel like their politicians are responsive to their needs. Try it: write a letter to any representative and you'll get a letter back that looks like it was written by them. I know because I used to open those letters when I worked (briefly) on Capitol Hill.
