It doesn't. Lol.
I don't know why people on here are adamant that Apple are going to purposefully hold back anyone's order. It's in their best interests to get all the stock they can make out to the customers as quickly as possible.
Just for pure guessing sake (and a bit of boredom) imagine 2 million people did pre-order. Imagine 500,000 of them were in the first 3 minutes.
The population of the U.S. is 300 million, in Europe it's 700 million, in the UK it's 60 million.
Based on a rough ratio, that would mean so where between 10% and 20% of the 500k pre-orders are in the UK!
Now, speaking from a business point of view, wouldn't it be wiser to make sure those 50,000 UK packages separately (probably in a few days or so) and then move on to another batch?