True - but this has always been a feature of the US system. Although a new president is elected in early November they never take office until January, the previous incumbent always remains president in that interim period.
Indeed. We have to remember that the USA is a big country and it has always taken a long time to gather and count all the ballots. In fact, according to Wikipedia, until 1937, they used to hold inauguration day in March. Don't forget that when the system was set up, the USA covered an area vastly larger than the UK and the fastest means of transport was a horse.
And while I understand this seems mighty odd for Brits used to an election and a new PM the following day moving into 10 Downing St I can see some advantages of the US system. First it allows for a more measured and smooth transition phase (well it normally does, I'm not sure this is going to happen this time). But it also has some attractive features for the actual democratic process. In the UK if you need to vote by post you have to do that some days before election day as you vote cannot count if received later that the polls close, regardless of when you posted it. So it there is a major issue that emerges on the eve of a poll that won't be reflected in the postal vote. In the US (in many states, remember each state runs its own poll) as long as your postal ballot is post-marked on election day or before it will count (unless it takes crazy time to arrive), so even if you have a postal vote you can make your decision at the same time and with the same information as if you voted in person.
The British system was designed - or evolved - in a situation where the relationships between the parties has always been adversarial. The transition is designed to be short and sharp and has the advantage that the outgoing administration that has effectively been fired by the British people doesn't get to continue to govern even though they no longer have a mandate. I think that advantage outweighs the disadvantage that some people voting by post might regret their decision due to events that happen after they post their ballots.
This could never work in the USA because the top level of the civil service is filled with political appointments and they all need to be replaced. That takes time.
