I think there's a lot of that in 40K though so I don't see why having a couple copies would be bonkers. Not to mention it has C:SM stuff in it... seems logical to have 20 copies on the shelf at all times right there.
Do you have any idea on the expense involved in having 20 copies "just there" at all times, in all shops, in all countries?
There are about 350+ shops worldwide.
Lets say the margin on GW products is about 60% so that means it costs GW 12 quid to have the book in the shop that works out 84,000 pounds of stock that doesn't move. Depending on demand you'd probably need that much again to be in transit and that much again to be in production.
So to keep 20 copies on the shelf GW needs to have 250,000 quid laying "dead"
When you do the maths the reasoning behind order only becomes apparent, particularly for items that are uncertain as to their market acceptance.