Zavvi's antiquated system does not do real-time stock allocation (as in, their website never knows how much stock they have left automatically), which means you could place an order for 100 if you wanted, just that 71 would be cancelled by Zavvi after you did (assuming there were 29 left available).
Yes, bought it from the link I originally posted.
I'll take pics later so you can see, it may well be that Zavvi only had 30 of them as much as anything.