Stop me if you've heard this one: Two guys are sitting in a Starbucks. One is tapping away on his Macbook Air. The guy next to him is busy pecking as well, on a keyboard attached to his iPad.
Yet only one of these two are considered to be on a "mobile" device.
If this were an isolated incident, you could conclude that yes, sometimes, the way we use tablets and laptops are pretty similar. It's not. Study after study shows that only a small minority of tablet owners connect them to cellular networks. That means most of the time most are employing them within Wi-fi range. Translation: They're using them on their couch, often in a reclining position.