If a commute takes 1 hr and that is a time of day when you typically have peak productivity/ mental energy then one is hardly likely to want to just sit there in silence. Do you not think that if you were in prison you might want pen and paper at least?
Well, that might depend on the commute. I'm on the train from 8:20-9am, and I've not yet had coffee, so there's no productivity to be heard of there, and at 5:20-6p the productivity tank is definitely empty.
Perhaps the morning side could, if I were awake. Although, on the afternoon commute, I read stuff such as on HN because I am mentally spent. (Though if it's too rigorous, like a deep CS paper, that might get passed over.)
