Arguably, laptops and smartphones aren't necessary. They provide convenient, mobile computing, but most people could get away with a standard dumbphone and a desktop if they really had to. I had to do it myself for a while when my MacBook Pro was stolen, and then weeks later, my iPhone. It was inconvenient, but I managed long enough to hold out for the newest versions of each before replacing them.
But just like a laptop and a smartphone: An iPad is a nice, really useful and convenient thing to have around. Without one, you'll manage, but for some people, it's worth every penny to buy and use one.