Dused wrote on 10/23/11 at 11:08:40:

They do:
order now and if the Amazon.co.uk price decreases between the time you place your order and the release date, you'll be charged the lowest price.

When I remember reading this last, I swear it worded it as if you'd get the lower price if the price when released was lower than when you ordered, you'd get that, but if it went down, then back above your price you'd get your price.
Hope that made sense..
Anyway, thanks for reminding me about their guarantee so that I'd understand properly what it meant