When is VxWorks inappropriate, but QNX appropriate?

EDIT: http://www.embeddedrelated.com/showthread/comp.arch.embedded... says:

> the most fundamental difference between VxWorks and QNX is as you have described, QNX lends itself to a message passing architecture while VxWorks lends itself to a shared memory architecture.

>

> My personal opinion is that a message passing architecture is easier to get to grips with and as such is potentially easier to understand and debug.

> However, the majority of software engineers with experience of an embedded RTOS will be very well informed about the Shared Memory architecture.