I'm sure there is. But by far, most businesses still need laptops and proper desktops to work. Sometime you need a big screen. Most of the time you want to have a keyboard, a good one, to type fast. You want to have the precision of the mouse of do things on screen. ANd you need power. A portable device, no matter how good it is, is constrained by ventilation, temperature limits, processor speed, space, and so on. For the price of an iPad you get a much more powerful desktop computer.

Tablets have advantages as consumer devices, as presentation devices, as "reader / browsing" devices. They are convenient. I do not deny that. But they simply won't replace everything else.

And the reason why the iPad sells so well is because it's a disposable device at heart. Whenever a new iPad comes out, most of the previous iPad owners drop their older version to get the new one. (same for the iPhone, by the way). Usually computer users keep their PCs active for way longer than that.