Because of this, you should think of Windows RT as the tablet, stripped-down version of the Metro portion of Windows 8. Windows RT tablets are more like the iPad -- mobile devices, rather than the full-fledged computers they look like. By contrast, Windows 8 essentially is two operating systems in one: the new Metro part that Windows RT also has and the Desktop part that is essentially a version of Windows 7. The Desktop in Windows RT isn't the full Desktop environment, but just enough of it to run the preinstalled Office RT and Internet Explorer 10 RT.
For more details on Windows RT vs. Windows 8, see Paul Thurrott's article on how to choose between them or my basic writeup of the difference between the two Surface tablets.
Windows 8 tablets and laptops will be more capable, but they'll also be more expensive. The Surface with Windows RT is competitively priced at $499 for the 32GB model, and it might be more energy-efficient because it is powered by an Nvidia ARM processor rather than an Intel processor. So you might still want Windows RT -- as long as you know what you're in for.