Fundementally, a tablet is a hand held device designed to work with a touch UI. A Laptop is designed to work with keyboard and trackpad interface. They are very different devices that overlap somewhat in functionality.
Hybrids (Laptops with touch screens or Tablets with attached keyboards) are trying to find a market, but it is a tough proposition, since fundementally different UIs require different operating systems and hardware. So far, these hybrids have largely confused customers with a hot mess of options that don't particularly do anything well.
Eventually, these form factors might merge into something useful and compelling to consumers, but it will probably require compromise of wieght, portability, battery life, cost, etc.. However, with so much content pushed to the cloud, there is less reason for a single hybrid device, since folks can access their information seamlessly on multiple devices.