Should clarify that I say two hours
per day above. I don't think I'd spend two hours going thirty miles, or even necessarily choose a job that involved
driving thirty miles every day.
But thirty miles in an hour on urban/suburban rail isn't particularly unusual. And this time is time you can use, if you have even a little bit of method about it. I know people who have done all the reading for entire higher education degrees in that period of time.
At any rate, the notion to which you're responding regarding the area of possible commute being 2800 square miles is foolish. You have to go to where the jobs gather, and there are all sorts of complex reasons why they don't distribute evenly across that area that a rational person should not spend time weighing up when they consider whether an iPad might be a useful thing for the train.
In my case, if I made the commute into London on a daily basis, knocking down the distance to this hypothetical US average of 16 miles might save, I think, about a third of the journey time in practice. It would knock off half of the price of a season ticket, which might be useful. But it would add easily 40% to the cost of a house, which is the overriding concern. And even then I'd still buy the iPad for that journey.