the manual says that because 10 w 30 motorcycle oil (which is designed for wet clutches) is what yamaha recomends. they sell some called yamalube
basically the oil that goes in there doesnt actually lubricate the crank like a car , it only lubricates the transmission, and clutch, gear saver is what my local ktm dealer recomended for me to use, and i heard on here that a lot of people praise it so it was a no-brainer.
the oil that you use in your oiler or whatever you premix with your gas is the actual oil that lubricates your crank.