Today I found a rather interesting article. It seems that I'm not the only one wondering about the actual purpose of the tablet. The article's author describes very well the initial dreams: a portable computing device that would do everything we need on the go.
Somewhere along the way the dream got broken: the freedom of portability got hijacked by relentlessly money hungry companies. Their dream was less poetic: whoever buys the tablet must consume what he is told to consume, buy and install what they are told to. Don't do more that the companies tell you to do.
After all, consider the PC: the computer users are spoiled. They can install programs from a variety of sources by default, no hidden options to check. They enjoy true multitasking, switching between media consumption and productivity tools with one click. Need a better OS? Just install whatever you want, you'll still get the warranty on your system.
Tablet users are prisoners: apps must come from a closed app store which is tightly controlled, if you want to break free you need to forget about your device's warranty (it goes out the window when you install Cyanogen instead of the official ROM). Multitasking? Forget about it. One app in the foreground is all you get. When Samsung brought you split window between two apps from a small selection, Android users called it a revolution.
Tablet usability is right now closer to what MS-Dos was offering back in the day. Well, you don't need to type commands in there so perhaps it's closer to Windows 3.11 (networking, baby!) but having just one window at a time.
Productivity is still a dream. You can't create complex presentations or ever run a fully operation development environment of a tablet. The computing power is there, more than necessary in fact, but none of the systems currently on the market allow that kind of freedom.
Tablets are powerful devices, kept in check by greedy entities working to herd users into consuming, not creating.