Still, it seems weird to put those into different categories. There could be a PC maker creating expensive PCs that don't compete with netbooks. In fact, there probably are (for example creating high end PCs for architecture and film editing). That PC maker would not be cannibalized by netbook sales.

Maybe if it is Microsoft vs Apple they are talking, but MS also sells stuff for netbooks.

Also, if there were no netbooks and no PCs, there probably would be more Apple sales. So Apple loses sales to PCs and therefore also to netbooks.