I am just a hobby builder, so I have a lot more flexibility than those of you with businesses.
But I also really appreciate a heads up if an item is back ordered.
One of the great things about Tackle Warehouse is that they show you on the site if, and how many of, an item is in stock, so you can order accordingly. If I go ahead and order it anyway with some other stuff, they ship it separately when it does come in, with no extra shipping costs.
For me, it is a small thing, and a back ordered item is just an inconvenience, but for someone with a business to run I can see how this can be more than just an inconvenience.
Having said that, I have no idea what is involved, software-wise, to get an out of stock flag to appear on a site's shopping site. I imagine it's probably expensive to have to get it changed, once it's already installed.