looking at it from the other side of the counter Roughquest, we are trained to ask foir the nectar card, if we don't ask and then the customer remembers after they have completed the transaction, it holds up the queue to add the points onto the card afterwards. In a survey of customers, on of the top suggestions was that the card was asked for, as many customers forget about it.
As for the account card, the staff are also trained to offer the card, because it is important to establish a solid customer base in any business, it is an effective and popular way of securing customer loyalty.