If a US dealer has an unsold car in the order process, he can assign it to a person, and the wait to get one built may only be literally days before that starts. If the order is entirely new to the system, it will take a lot longer and probably similar to what is being seen elsewhere in the world, and shipping times would also come into that (it takes a lot longer to get to say California than it does to the UK! from Germany). But, given that there are still unallocated vehicles coming into the USA, one of those may be assigned to that order, and it could show up early if the build matches what the customer wanted. Until or if the situation gets to all of the vehicles landed have already been sold (probably like in the UK), someone in the US will probably be able to get one quicker. Give the situation a few months...the first i3's were only delivered here in early May 2014...in six months time, the situation may be quite different. It is going to take BMW longer than that to expand production much more, and who knows how the demand will hold up.
It's the same thing with any popular new product. But, as opposed to say something like a new iPhone, you can't store a bunch of them in the warehouse prior to the first sales day...the cars take up too much room, and the capital costs are a bit more per unit! The profit margin is a lot different as well.
