Yep as we understand it that is correct. Very odd indeed.
Either damn stupid and expensive to build and fit 2 different sizes of tank or there is a good 'Engineering' reason for it.
Maybe it's a 50ltr tank with 10ltrs blocked off?
Maybe weight related? Less powerful engine and 10ltrs of extra fuel to pull?
Could be that 'Marketing' got involved and didn't want the car to go too far between petrol stations so lots of other drivers filling up see the New Cooper and want one.
Its a shame as we are talking 530 vs. 430 miles range if the Cooper had a 50ltr tank. We just think the Cooper can't be seen to go further than the 'S' on a tank. Down to the 'Marketing Department' we think?
It's a pity for us as we are having an Auto which probably won't be as fuel efficient as the manual (no data published yet .... as far as we know!) so 50ltrs would have been great.