This is extremely difficult to convey to non-developers though because they often look at software as a house and think "there's tons of houses (ecommerce sites) built every day and it's down to a science - how hard can a house (ecommerce site) really be", but miss out on the fact that all houses have pretty much the same structure of a foundation, framing, wiring and plumbing, and a covering of paint and a roof - this is largely kept consistent and we'll implemented by building codes.

I can only speak from my own experience, but every single web application I've worked on has had a wildly different structure than the others and the only consistent thing between them has been endpoint routing mechanisms.