AMS: Frankly, UDMA and Giga*bit* are driver issues, not OS issues. It's just there's no gigabit hardware for older machines. There's no support for PCI for similar reasons. I've not had much experience of the competing USB stacks, though. What features does Castle's lack? Last time I looked, it appeared that Castle's didn't even do HID properly.
It's nice that you know how far ROL's RISC OS is away from being completely 32bit. Other than that, Realist does seem quite vague and sensationalist. Although I'm not sure what he said classes as slander.