Well, the Apple Store manager just knows that his employee missed an "accessory" sale - AKA, things to boost the days profits. I'm guessing the Apple store isn't any different than working at say... Best Buy.
There is a reason that accessories are "pushed", aside from ensuring the customer does NOT have this experience upon arrival at home, they also boost the numbers.
I would have also probably have needed the reminder at check out.
And really, is it any different than when my Dad bought his Mac Pro in the store, spent over an HOUR with the sales guy going over specs and making sure he was getting what he needed... and then the guy neglected to mention it didn't come with BT or Wireless? And then, it needed to go back to the store to have it installed (60 miles away). My Dad was a switcher with that purchase (and also bought my laptop on the same recpt along with his 23" ACD, it wasn't a small purchase) and never thought it wouldn't have that card in it. All his Sony's had had that basic piece for years.
The salesperson dropped the ball then..... same in this case. He was a nice guy, helped my Dad greatly - BUT, for one important piece, well, really just blew it.
ANYWAY...... Apple has always been more than fair to their customers when they aren't happy. In the words of that Corporate Customer Service rep i spoke with last year.... "We here at Apple know that without our customers, we have no jobs."