Don't see any such ban on the Delta webpage. In fact the following is the blurb on delta.com about PED
Portable Electronic Devices
Devices containing lithium metal or lithium ion batteries (laptops, smartphones, tablets, etc.) should be transported in carry-on baggage and not placed in checked baggage.
When that is not possible: the devices should be completely powered down to the OFF position (they should not be left in sleep mode), protected from accidental activation, and packed so they are protected from damage.
Notice the when not possible portion.