I don't buy that. If that is the case then why didn't they ask the guy behind you? How come they don't ask every-one all the time?
They ask because it is their job to ensure a flow of traffic and by asking if X has Y in sight they think they're doing a good job. Problem arises when they ask Z if he can see Y and Z says yes when really he's looking at X. Two aircraft now following X. Recipe for disaster!