I sometimes feel bad having to order a 3 cent part at Farnell/Element14. Which is then packed and shipped from the UK to the Netherlands without any handling or shipping fee. Usually it is delivered within 1 business day.
That said, they are treating a 3 cent part equal to a 100.000 dollar piece of equipment, which probably makes financial sense for them. Its the consistency that I, as a professional customer am willing to pay for. Farnell has become my one-stop-shop when it comes to parts and tools, I may be able to get something cheaper elsewhere, but the convenience and speed make up for that.
I could imagine either dirt cheap labor in well laid out warehouses or some form of automated picking solution.
i'd love to see a proper dive/writeup from someone in-the-know. lacking that, here's a third, completely speculative theory:
from what i hear, these big distributors are excellent at providing quick turnaround time. suppose that in order to guarantee this for large customers -- who presumably provide the bulk of revenue and who most value this service -- DigiKey must continually over-provision its operations. and so whenever there isn't a number of outstanding rush orders, there's extra staff available, at no marginal cost to the business, to assist the little guy.