As I am not British the origin of the ARM, or RISC OS is utterly moot and has no influence on me. Hey I use Delphi and like it (and that's from the US).
Java runs on a virtual machine and no one (that I know of) calls it an "OS".
The native PC hardware does not run RISC OS as it's OS (which you've already conceded). I'd also point out that the PC can continue to run Windows even if the RISC OS emulated by the VARPC crashes - the converse is *not* true. Emulation is the faith of dead platforms like the Spectrum and the Commodore 64, if saying RISC OS is still an operating system on a PC even it only runs on a sophisticated emulator (aka virtual machine) makes you happy fine - who am I to argue !