In other words, does the iPad REALLY fill some USEFUL need that other products don't do better/more practically?
Depends on your definition of REALLY and USEFUL. From your prior posts, I'd say that the answer for you is "no, it doesn't", and you're just going to argue with anyone who does find (for them) a really useful use for it.
Go into the average home and you will find it littered with products people don't need but they bought it anyways. Most of the gifts people receive for special occasions and holidays they don't actually need but they just want it. The average American does not need to consume 3000 calories a day but they want to. Many people don't need to drive an SUV but they want to anyways. Most people on this forum did not need to buy a Mac, they simply wanted to. Users on this forum easily spend $1500 on a notebook that they don't need but buy it anyways. The iPad is no different, many don't need it but will buy it anyways. I'm sure you have items that you bought that you really did not need but purchased it anyways or could have found a cheaper alternative.