I didn't go through every version, but I confirmed that Requestor shows up as an option from at least 6.2 SP2 on. So, on the surface, it looks like an in-congruency in the documentation. Mary Carbonara, I'm not sure what our policy is for addressing documentation issues going this far back, but raising to your attention.
Lastly, I'll see if I can find a good example of the use of Requestor level. If anyone in the community has one off the top of their head, please chime in.