I guess it might be airline policy. Where I work, we have to check flight numbers, dates and even times. Check the names (Mr/Mrs etc) and finally seat numbers so we can direct the passengers.
It still scares me how many people don't check all of these details and simply glance at the seat number. If I'm at the door boarding and the checks aren't being done properly by someone else, it's still my arse that will get it.