Well, if it is said below average it just mean that it will take a lot longer to achieve your dreams to reach your minimum withdrawal, but it doesn't mean that it is impossible to mine.
Right now as the difficulties increases we might have to check how it is calculate. It is much different now compared to a few months back when even a Dual core can reach a minimum withdrawal (for BCN) within 1 week.
XMR takes a longer time.
Hope this helps?