DocOc, you asked if an OR nurse does a head to toe assessment earlier. When I started in the OR I wondered why they didn't either. The reason is that an OR nurse performs a focused assessment. The OR nurse is concerned about positioning, metal in the body, NPO status, allergies, possibly labs depending on the type of surgery the patient will have, SCDs/TEDs, any lines in place, if the patient is to be admitted or discharged postop, need for blood (along with appropriate samples taken to expedite getting blood), etc. It's like when you were in nursing school. If you had a test on the diseases of the lungs, you didn't go home and study labor and delivery. You focused on what you needed to know and used your ability to gather pertinent information and even some past experiences (maybe your own weakness or mistakes you made before) to prepare for the task at hand. While it is nice to know as much as possible, it is best to know the information that will most likely affect your patient during surgery.
When you mention patient advocate, you are right, anyone could be one. I have worked will OR RNs who make me embarrassed to share the same title and have worked with ORAs and STs who I can't learn enough from not only because of their skill but their ability to work as a team, allowing their experience to lend itself to ensuring that the surgery at hand is the best it can be. The same can be said for surgeons/doctors though. Each individual decides who they are going to be and how they are going to perform, their title does not do that for them. Having an RN in the room, I believe, is to ensure that another trained person is there to catch mistakes, to critically think when a situation occurs, and has the licensure needed to perform certain tasks. Mistakes and events occurred routinely enough to make an RN in the room required for surgery.