Who is responsible for sustainability in IT projects?

After I got very worked up again yesterday about people asking for "quick help" in setting up something and nobody thinking about the long term sustainability of IT operations I would like to point out a few facts about this topic:

The major part of IT project costs are not related to the initial setup!

Operations, maintenance, updates, bugfixes, application administration, backup and disaster recovery exercises make up the majority costs and should not be neglected in the initial planning.

Actually, the more a project is meant to be temporary, the longer it will run and the more it will cost in the end.

To underline my personal beliefs in this matter I found the following links on the Internet, I am sure that with some time on Google you can find even more:
Therefore I would like to suggest to alway strive for a simple solution and take the follow-up costs like maintenance, updates, security fixes etc. into account during the planning stage.

This is also a golden opportunity to include the original requester in the discussion about TCO and about who will actually spend their time on the follow-up tasks.