It depends on the age. In the last few years, they went with an Eco bowl, there is an E instead of an S on the part number. The E bowl works with either tank, but the S bowl needs the S tank.
The tanks porcelain is the same, in the tanks case, it "is" the flapper and fill valve. The flapper is weighted, and the fill valve is tuned to shutoff sooner so it doesn't keep overfilling the bowl.
Homeowners that use a Fluidmaster 400A fill valve can wind up overfilling and wasting a bunch of water.