guestx: "This lack of adaptation is a crucial reason why RISC OS isn't regarded as a primary platform for most users and developers these days."
Sorry to question accepted wisdom, but actually it's a reason that was of little or no relevance to most of the users concerned.
The majority of NeXTstep users (with certain important exceptions...) moved onto Windows 95, 98 or even 3.11 platforms, and the fact that they were moving from a microkernel to a DOS-based operating system probably wasn't the uppermost thing in their minds at the time. Equally, desktop Acorn users who left the platform after the demise of Acorn, were probably not moving to NT 4 as their desktop OS.
In both cases, the users concerned were moving for reasons of features, support and supportability, not underlying technical aspects of the operating system concerned.