Re. vulnerability, I would suggest that the Wintel platform is less likely to die than the real ARM hardware. On that basis, ARM hardware draws RISC OS users away from the "safe" option.
Wintel/DRM licensing will always be cheaper than ARM motherboard development. So ARM hardware also draws users away from the lower-cost, higher-performance option.
Now I am not saying that is all a good thing, but it does seem to be an valid angle to consider.
What users want is to be able to choose the best hardware, then choose the best desktop OS regardless of the hardware, then choose the best apps regardless of either.
RISC OS should aim to be the OS of choice on as many platforms as possible: roll on VA Mac and Linux. And it should make migrating apps across as easy as possible - roll on the Unix Porting Project too!