Thanks for starting this thread - it inspired me to do a little research on my own which led to a discussion with my wife.
Basically I told her there was much more to this passage than the predictable, canned WT response. According to bible commentators, there a multiple ways of viewing this verse: (1) it could have been a human messenger of Peter, not neccesarily angelic (2) it could have been a guardian angel according to one of the Jewish superstitions at the time (3) according to another superstition, you might be visited by an apparition of a person who is about to die which presages their approaching death (4) it is Peters ghost (5) the lame WT interpretation.
So, I asked my wife Why don't they mention any of these other ideas? Well we came up with a few reasons: (a) the society does not want to cast doubt upon the beleifs of those "early Christians" and they want you to think first century Christians were all part of one cohesive, united religion, which any true student of that time knows is false. (b) they keep it simple because they don't want to confuse dumb people. Here's your answer, that's it, think no further (c) they want to reinforce their own worldview and doctrine and thus feel the need to disambiguate this passage.
My wife was impressed. I said There's a big and endlessly fascinating world out there outside of WatchtowerLand.