is it in the seals? I presume as long as you've the spacers either will fit any shimano h11 chainset ?

I *think* I know the answer to this one, I replaced the Hone crank on my commuter with an Alfine one recently

the tube that fits between them is a different length (road bb shells are shorter, mostly) but the cups appeared the same (although, indeed, perhaps the seals were different). I had to change the spacers aswell as the BB Axle length was different.

I was wondering this too, IIRC most road BB shells are 68mm, but CK BBs are also road or MTB version, so is there something else different? Is the axle on MTB chainsets bigger?