Optical disks are more and more becoming redundant. Literally. Given the volume of applications being delivered on line, rather than on optical disk, most people rarely, if ever, need an optical drive for updates or initial installs, and Apple is acknowledging this change. And yet, for all the models you noted, an accessory DVD drive is available. For those who might want one. To share between multiple devices and users, for that matter.
6/11/12 at 5:14pm