that "ride on flat tubular" is just a myth, plain and simple. It will wreck your rims.
Granted, a well glued on tubular offers a very subtle ride. For the rest of us - try changing a tubular in a pouring rain in order to get home, I´d very much like to see your effort.
Oh yeah, when a tubular comes off rim whilst skipping a fixie in traffic it´s just such a RUSH!