I think that is the reason that turning cylinders would be more common. You can use a lathe. To do the bores in the block you need a mill. I think the lathe and the knowledge to use it are more common than the mill and the knowledge to use it.
I never realized before though that there would be a reason to chose block over spigot machining. The idea that the block can be used with any number of cylinder changes now is a definite advantage in my book also.