It may be less than you suspect because the regular bubble in their ordering pipeline might give them time to deal with suppliers, maintain stock, improve their website, maintain systems, relax and refocus, etc.

I doubt it works out better than not doing it at least economically, but there may be enough benefit to offset most of the costs.

The times I've run into the B&H sabbath outage, I just waited and ordered later. There are more thing in my life than just ordering things as fast as possible, and I respect a business for having other priorities. (Plus, B&H is just generally a really good supplier)