No, seriously, why do they? It's not like the construction workers don't get paid their wages if they aren't given such projects, and, unless you are buying the resources from overseas, the only cost for the construction materials for the state is wages/salaries of the workers who are involved in the relevant processes.
Am I being swindled?
You do spend a lot less money if you do have other cities under your state, but that's usually not the case if you start a new game on a random map though. You can set up a custom map with a starting city tho (it's sometimes hard to get to a stage where sewage works on an edit-map since you can't test the sewage system as you go along)