Inspired by this
I am Ricardo Lopez, Test Manager for Surface RT. After the OS, OfficeRT and a bunch of apps, you will still have more that 20GB. As you say, you can always add an SD card and while you cannot add apps there, you can get music, movies and photos there.
That Reddit comment is referring to the 32GB Microsoft Surface RT. Assuming everything, that means that Windows RT, OfficeRT, and a few small apps, the "light" version of Windows 8 requires around 12GB.
Does anyone have any data as to how iOS compares? How much space does iOS require?
I know that it does not cut into the storage allocated for the user (i.e. a 16GB iPhone will offer almost that much to the user). Data on iOS 6 is preferred.