I don't know if this is for a good reason or not, but Apple uses `NSUInteger` in all the definitions that I've seen. I think it's almost better to just always use `NSInteger` and the like in place of the straight primitive (even here, where the bits are important) so that way you can have a blanket policy and not really have to worry about it. So 64 bit will have more bits -- it doesn't really harm anything and allows us to be consistent.