There has been similar changes in their European operations some months back. Many items are no longer covered by complementary postage. Deliveries also seem to take longer to 'ship' (that might be my imagination though). I think it's all related to Prime, them trying to make a subscription service look more valuable by disabling the alternatives.
Yup, a few months back amazon uk went from "free shipping for everything" to "Ah, only if you spend £20" (I think? perhaps £25) which is how it used to be way back in the day with their "super saver" delivery.
I'm amazed it actually took Amazon so long after the demise of Play.com to do this. (Play.com were a serious competitor for games/music but had a tax loophole closed on them.)
£10 now, which isn't so bad. I'll usually wind up manually combining orders to get above threshold, but sometimes it does mean that I won't order from Amazon at all.