People need to remember that Windows 8 and Windows 8 Pro are different SKUs of the same product.
"Windows 8" refers to the "Home Premium" equivalent, this time around. Both are still x86/x64, however.
Windows RT is something entirely different, as the version that runs on ARM. Also, for what it's worth, Windows RT appears to have the same pen support if a hardware vendor decides to use a true pen digitizer. However, so far, none of the OEMs have chosen to do so, most likely to keep cost down, I'd bet.