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When we think about a shutter, we think of the old school shutters.. a lot of people don't realise what it looks like in modern cameras.. and I think that's a big reason why people get confused when learning about rear curtain sync.
Here's an excellent video that shows the full process.
http://www.youtube.com/watch?v=6x_YXj0vWVM
That does highlight why you won't want to use rear-curtain flash when you're at max sync speed. Then it becomes mid-curtain flash!
I'm baffled why they still choose a mechanical shutter. Didn't one of the 1-series bodies have electronic shuttering? I'm amazed that hasn't propagated down the line. Electronic shutters can trigger sensors on the order of tens of microseconds - that's 1/10,000 shutter speed... Is it a problem switching the charge wells for such large pixels?
The original 1D had an electronic curtain, I think. But that was with a CCD sensor. CMOS take a long time (relatively, of course) to flush, meaning a mechanical second curtain is essentially a requirement. Current cameras do use an electronic first curtain, as a silent shooting mode, or with Live View.