For example: how many people use Microsoft Excel at least once a week? 100 million people? 250 million? It's certainly a large chunk of the computing public. These are sophisticated users of desktop software, and I can't imagine they'll be putting down their Windows PCs in favor of iPads.
Lately, HN-types have been suggesting that there are two classes of users: the sophisticated software engineer, and the unsophisticated masses. This is both insulting and wrong.