This is true. I actually worked with the "service" at Amazon that made these decisions. For a company with a single warehouse, or even multiple warehouses with

This is true. I actually worked with the "service" at Amazon that made these decisions. For a company with a single warehouse, or even multiple warehouses with equivalent inventory selections, you shouldn't face this problem. But with Amazon, where the entire inventory selection couldn't even fit in 20 warehouses, you end up with a terrible NP complete problem whose solution quality can make or break profitability on pretty much any product with less than a 10% gross margin. And I say "service" because you can't really fit into a service oriented architecture when you have solve times in excess of 5 minutes...the "service" is really just a way of dumping problems onto a queue to be passed downstream when done.