[steveylang]

It only makes sense for Deckard to be a replicant — something that Roy would know, and choose not to tell.

Maybe I should have recognized this earlier, but I really like this point and feel it adds depth- whether or not the screenwriters or Ridley Scott even intended it. It's not necessary for this to be the case for Batty to spare Deckard, it's also possible that recognizing his end was near he wanted to pass something on and/or communicate his life in some way to another.