We know that tablets don't leave home too often.
Therefore, I expect the number of offline videos to be low: I mean, if around 80% of the time, the tablet is at home, why to bother? You can use the high-speed network your own house is connected to.
If tablets don't leave home, the only time I see it viable to store offline videos is on long journeys. I expect people to pack one or two films they want to watch, perhaps a few episodes of their favourite series.
Also, it's inconvenient to upload movies to an iPad from the laptop. I've never bought a TV-show from iTunes though...
When I was traveling between Berlin and Budapest on a monthly basis by train (much better than airplane: comfortable bed, electricity, departs and arrives to the heart of the cities), I used the iPad as the travel device: although, honestly, I mostly read books and/or listen to music.
On everyday commute, based on the statistics, smartphones are the way to go: even if they offer smaller screen, they're less bulky.
But as samsung is definitely blurring the line between a tablet and a smartphone, with offerings on every two inch (3", 4", 5", 7", 10"...), we can't know exactly...