Not particularly wanting to take this off-topic, but hey, it's in the forum now...
Absolutely, the perceived responsiveness of RISC OS now is due to the lightweight multitasking model. This means that software has to be written to do very, very little in between every poll. In the future, if we go down a data-intensive route in our apps, we may find this being stretched.
Already, when I use Netsurf, I notice this. I tend to browse in multiple windows. So I'll load up a page, and keep bringing up links off that in new windows and sending them to the back to load. It's a trick I learned in my old dial-up days, so you can get pages and pages of stuff loaded up then disconnect.
However, with Netsurf, because it doesn't poll while it's rendering, every time it finished loading a page it freezes for maybe half a second. When you've got ten pages loading simultaneously, this is quite noticable.
Now it's only half a second, and that's no biggie. And if I were to have a computer from this millennium, it'd be ever quicker. But my point is that as we start to interoperate with complex, large data structures (such as complex web pages) we might find RISC OS' simple multitasking model being stretched. We shall see.
Of course, RISC OS' simple multitasking has led to the development of lean, efficient data formats in comparison to certain other platforms, so it's not all bad.