The City Council shall never authorize the expenditure of public funds for the development of a privately owned subdivision. In this section a subdivision shall be deemed to be privately owned when the owner or owners, whether individual, partnership, corporation or other body, shall have filed a plat as required by this Charter, and shall have undertaken the sale of lots or parcels from the platted area. The prohibition herein shall not apply to extension of utilities or services to any incorporated area for the purpose of serving existing houses, housing facilities or commercial buildings.