I will say, in the OP's defence. I placed an order on Friday (14th) and on all the screens I was shown regarding delivery did state the 15th for due delivery. It wasn't until the third email (Order Comfirmed, Order Shipped, due delivery date) that I was informed that it would be Monday 17th before my order arrived.
I knew I wouldn't get it till Monday 17th however
Maybe an addition to the standard confirmation email stating that orders ordered via next day on a Friday won't arrive till Monday unless Saturday Next Day has been specified would be in order?