According to the Chicago Sun-Times, Dave Awl, author of “Facebook Me! A Guide to Socializing, Sharing, and Promoting on Facebook,” said, “This is Facebook’s sneaky way of trying to get people to use the Facebook email more often. If Facebook is your main email, that increases the amount of time you spend on Facebook, and the more ads Facebook can sell.”
But Lifehacker says it’s easy to return to your old email address. First, click "About" on your profile, scroll down to your email address, and click "Edit.” Then click the circle next to your Facebook email address and reset it to "Hidden From Timeline." After that, click the circle next to your other email addresses and set those to "Shown On Timeline." Finally, click “Save” at the bottom of the Edit popup.

Twitter
Myspace
Digg
Del.icio.us
Reddit
Slashdot
Furl
Yahoo
Technorati
Newsvine
Facebook