Interesting thread (I've been traveling, with limited web access, so I'm just catching up). As I'm getting older, I'm no longer the best person for a "hasty team" (maybe I should join the "old slow guys" team?). Consequently I've been taking some training in SAR management. My comments are from that perspective.

Regarding ending a search without finding the subjects, that is probably the most difficult and painful decision a SAR manager can make. As Teslinhiker points out, resources are often limited, particularly in small and rural communities. In most areas by far the bulk of the search people are volunteers who are taking time off from their families, jobs, and other pursuits. Volunteers don't get paid for searching. How long can one ask people to do this, when there has been no apparent progress in finding the subject? Ask yourself how long you would be willing to continue searching for someone you don't even know?

When all the likely areas have been thoroughly searched without any clues being found, then what does the search manager do? In rugged or thick country there is always the possibility that they are still in the area, but no search team has been lucky enough to spot them. Do you continue to search the same areas repeatedly? Or perhaps you then conclude that they are outside the original search area? If you choose to expand the search area, then how far and in what direction? How big an area can you resonably hope to search with the limited resources available?

Finally, any search manager always has to keep in mind the possibility that the subject is nowhere near at all. They might have intentionally gone missing, and are now sitting on a beach in some foreign country sipping Piña Coladas. These case are thankfully rare, but they do happen.

Regarding ignoring clues, unfortunatelythat does happen sometimes. One of the issues is that those officials who have legal responsibility for SAR (RCMP, County Sheriffs, Alaska State Troopers, etc) generally have many other duties besides SAR. Searches make up only a small part of their responsibilites, and they aren't always well trained in how to handle these events in the early stages. Trained search managers often only get called in after the search is well underway, often for many days. Clues get lost or misinterpreted. Initial searchers (often untrained) sometimes unknowingly obscure or obliterate important clues. For anyone involved in SAR, either as a volunteer or an official, I would highly recomend some of the NASAR courses, such as FUNSAR or Managing the Lost Person Incident.

The bottom line is that we do the best we can with the resources we have available. Luck, both good and bad, always plays a part.