Microsoft’s next operating system, Windows 10, will launch Wednesday. Upgrading is a no-brainer. Critics say it’s better than both the loathed Windows 8 and the liked Windows 7. It’s also free to users who switch from those versions within the first year.

The stock is a good deal, too, although its appeal is less obvious. It has nearly doubled in price in four years. Results for Microsoft’s June fiscal year, reported this past…