No Senator is going to deny (or at least they shouldn't) that they use form letters and autopens on occassion--they simply would be able to do little else than respond to letters if that wasn't the case. Hopefully, most of them are a little more accurate in matching the form language with the intent of the actual email.
That said...there is a difference between sending a form letter to a constituent regarding a political opinion and sending an autopenned condolence letter to a soldiers family when you are the Secretary of Defense. Most Senators will "pull" certain letters to be hand signed--Rumsfeld should have been doing this for the condolence letters.