I think the previous poster is correct about wheel size/motor power.
I've just recently been given a Workzone (Aldi) wet/dry grinder and that also has the wheels at right angles to each other. The wet wheel is MUCH bigger dia and wider than the dry wheel. As someone said, the wet wheel must go MUCH slower than the dry, hence the need for a gearbox in this design. And it's a right angle gearbox otherwise the OA length of the machine would be excessive (assuming a worm drive, which is probably the most compact, and cheapest to make).
I'm converting the dry end on mine to a big (11 or 12 inch) sander as I already have another off hand grinder. I'm mounting it on a board with small "stops" each side (on a separate shelf/bench) so that I can simply lift the board and turn it through 90 degrees so I can use either end/side, as required.