I'd argue that Apple spends considerably more on the development of an iPhone than is spent on a typical defence project. For any product which is manufactured

I'd argue that Apple spends considerably more on the development of an iPhone than is spent on a typical defence project. For any product which is manufactured in large quantities, the BOM will account for the vast majority of the overall cost, so limits on the cost of the BOM will significantly constrain design decisions. These constraints are less significant for products which are sold in more limited quantities. Here, design & NRE costs predominate, leading to (very) different constraints on design decisions. In this situation, for example, it might make sense to buy a more expensive materials to make the system easier and faster to design. Software itself isn't homogeneous. Different software products may scale in different ways. Embedded Software is different from Enterprise Software which is different from Application Software ... and so on. Some commonality can be seen however. For example, product line engineering can be used to find commonalities and amortize design costs over a set of similar-but-distinct products ... although this is easier to achieve when you are doing bespoke work for clients than when you are producing shrink-wrap applications. Here, you are scaling up over multiple different customisations of a design, (or multiple different members of a design family) rather than individual product elements -- but it is still an economy of scale none the less, and it is still software.