Article: The Apple student discount

I'm looking at MacBooks at the moment as I'll be hopefully starting university this year. However, I have come across something rather odd. After trying to find my institution on the apple website I realised I don't actually have any student ID for it, so I tried to access the student pricing another way. And I found the student website, or at least I thought I had, as the prices were lower than normal. However I thought the discount was 15% off, but the price for a 13" macbook was stated to be £798 instead of the £849, which is definitely not 15% off. So then I decided to log into the apple store from my unidays account, which is verified by my college ID rather than my non-existent Uni ID. I found the price to be lower by this route and it was £729 for the same laptop! And this coincidentally is very near 15% off.

So if anyone can explain why there are two different pricings for "student discount" I would love to hear it...