Case-reed is a more efficient design. The reeds prevent the air/fuel charge from blowing back into the carburator on the compression stroke.
From piston-port to case-reed is a night and day difference in terms of performance.
Why cylinder reed intake? Ski-Doo claims this design has all the power of the case reed designs, with the advantage of being able to mount the carbs up on the cylinders instead of down on the crankcase. This allows for zero engine tilt, and an engine mounting position that is lower and closer to the drive axle.
Lowering and centralizing the mass was the objective to reduce the moment of inertia and improve the handling. This design change is critical to maintain vehicle cornering with today's long travel suspensions and the higher chassis center of gravity they create.
I believe they mean that because the reeds are in the crankcase on a cylinder reed motor, you dont need to allow room for the reeds to mount between the carbs and crankcase, so you dont need to mount the engine tilted to allow room.