Project Management Activities

Up until 2009, I was the "Systems Administrator, Windows, Cisco network, EMC storage and a host of other roles" for a variety of companies. Executing the technical task for an organization got to be a challenging adventure and in 2009 I decided to shift my track toward the Project Management role. Understanding the technology has been a great way to morph to the Project Management role. I feel that my background helps to effectively lead a discussion around a topic and to ask the questions of the current engineers. In this role I do not get to "experiment" with the technology like I used to and I am left at the mercy of the engineer to help fill in the activities for the latest and greatest. That is where our problem lies, engineers forget stuff or just plain don't think it is important to add it to the task list.
I learned that lesson the hard way today. After months of working on a project, we got the install done. Upon appearance of the web page, I exclaimed..WooHoo! To which I was met with, "Yea, but...." Which translated into a discussion about all the tasks that need to happen now that the web site is up and running. My fault. When I asked at the onset about the tasks that need to take place and produced the artifact that was agreed to, nobody ever said "Boo" about missing a whole bunch of stuff.
Wanting to learn from this lesson, I pondered how to resolve it. Option 1 could have included me installing it a home so I would know to cry foul early and often. Option 2 could have been to ask for more in person demonstration activities to which I would have seen all the steps they were going through. Option 3 includes accepting the new tasks and adding to the schedule. Looking back, Option 2 would have been the most effective for me.
What are your thoughts for gathering all the activities before embarking on a project?