Turning off devices during takeoff and landing is not so much due to any electromagnetic interference (in which case they would be banned at all times) as to ensure pax are not immersed in them during the safety briefing or stages of flight where you might need a sudden Brace or similar. Having them switched off for this purpose thus forms part of the Cabin Secure approach procedure, hence the TOD routine.
Anyone driving their car in cities will understand an increasing hazard is the significant percentage of the population who cannot do two things at once, and who now walk along the street completely immersed in their Iphone, Walkman, or whatever, and step straight into the road while still looking down at their mini keyboard. You don't want to have this sort of non-response if there's a sudden call for Brace due to a runway overrun on touchdown. In fact you don't want this person between you and the emergency exit at all.
I wish the same approach was applied to those who read newspapers or conduct loud conversations during the safety briefing.