[(myl) That too. But some approaches to the semantics of tense and aspect involve quantification over times; and in that context, the ambiguity in question looks a lot like the implicit restriction of the range of quantifiers. ]
This blog reminds me of all the headaches I got trying to follow along in my Intro to Philosophy class. They were almost as bad as the headaches I got trying to follow along in my Intro to Linguistics class!
I think it's semantic: "Lately" is vague, necessarily for the question or for the negative, but it's rude to say just "lately" when in fact you last saw him at a specific time and place, which you could just as well report: "Yes, I saw him yesterday; he looked terrible."
SQB, perhaps it is a difference of dialect; I prefer "recently" to "lately" in that sentence.
NM, I can think of situations where you'd prefer to say, "Yes, I've seen him recently, why do you ask?" rather than quantify exactly when and where you saw him. Your example is a likely response when chatting amiably with a mutual friend who asks, "Have you seen Bucky lately?" My response above is arguably more likely if, say, you're a fifteen-year-old responding to a furrowed-brow-hands-on-hips question from Bucky's mother. For example.
^That's what Satchel wants to know. Obviously at some point in the past, he has seen Bucky, but since Rob didn't indicate a limit of time in which Satchel may or may not have seen Bucky, Satchel is unsure of how to answer the question because he is trying to determine whether Rob intended there to be a time restriction on the question or not.
The descent into skepticism of the reliability of the senses and across about 3 other modes of philosophical thought is a nice touch. I've never declared a favorite Get Fuzzy strip, but this might just get that award.
Hidden intellectual depth shows up in the most unlikely places. We're all born with more or less the same equipment, refined by the same number of generations of culling, so much of the difference between people is more a matter of inclination than capacity. Dogs, perhaps not so much.