According to Apple SVP of worldwide marketing, Phil Schiller, the iPod touch doesn’t include an ambient light sensor, because it’s too thin to include the component.
Website iDownloadblog posted a reader’s email to Schiller. The user, who owns a current-gen iPod touch, said that they noticed that there is no auto-brightness setting on the device.
Here’s what Mr. Schiller had to say:
“Thank you for purchasing a new iPod touch. It is a remarkable device! The 5th generation iPod touch does not have a built-in automatic light sensor (it’s just too thin!)”
That’s probably a good reason not to have an auto-brightness setting.