OK, I admit, I'm a bit confused. The splined interface for the rear cog is also threaded to take a freewheel? So, when I feel the need, I can turn my 3 speed fixed hub into a 1 speed freewheel, and make it rather difficult to change back (removing a freewheel is never fun).

For once I'm going to be the one to say, why is this desirable? And I was all excited when I thought they had threaded the reverse side, making it a easily reversable.