Absolutely true. A tablet isn't as capable as a PC is, yet. Trying to do my taxes on my Nexus 7 would be a nightmare. But it satisfies a very good use case: a cheap, portable device for casual computing and media consumption. The only fundamental thing standing in the way of tablets completely eclipsing PCs is the input method. If we can get a good replacement for the keyboard/mouse on a touchscreen device, the days of traditional PCs could be numbered.

If you're talking specifically tablets, then you won't get any extra input methods - when a tablet is used, your hands are in a position that only the touchsceen can be used effectively and your other appendages are not that useful for input.

So either we figure out how to make touchscreen+voice to work effectively for content creation, or we'll have to use something other than a tablet experience for that.

Stylus. 6000+ year old invention for increasing positional and pressure control on touch-sensitive tablets.

The hardware is there already, but the stylus-optimized software is thin in the ground.

You're right about input. But I doubt a touchscreen will ever suffice for a lot of professional work.

For graphics and CAD work, I need the precision of a mouse cursor. My laptop's trackpad works great, and my mouse works even better. My fingertip on a screen, by contrast, will always feel clumsy in comparison. Fingers are just too fat. The only way they become not too fat is with a gigantic screen. But then that's not really a tablet. And gigantic screens can be ergonomically bad, because they force you to bend your neck looking at them.

Likewise, for serious typing, I need the tactile response of a keyboard. Touch-typing on a touchscreen is frustrating.

Of course, there's no reason you can't attach a mouse and keyboard to a tablet. But then you basically have a laptop that doesn't fold closed. It's hard to consider that a uniquely tablet-esque experience.