Read Sheldon's site carefully, and you'll notice he says that the spiders on 8, 9, and 10 speed cranks are the same, only the chainring width changes. He doesn't say this explicitly, but says that 8 speed crank spiders are the same as 9 speed crank spiders, and then somewhere else says that 9 speed crank spiders are the same as 10 speed crank spiders. Therefore, by the transitive property....