In reply to:

no president would take the chance that someone would eavesdrop on the prompting and record it.

Oh, really? Well, there's possible evidence on the White House web site. Watch this press conference (The link is to the White House website.) About 13:32 into the press conference, while Bush is listing off names of captured enemies, he mispronounces a name, and then seems to be corrected via earpiece. Watch how he pauses while looking down to the right, as if listening intently, and then blurts out the correct pronunciation.

Strange stuff here. I'm not entirely convinced, myself, but it sure would explain why he often has stange pauses while he speaks.