A number of good questions brought up on this thread. Here are the conclusions (not facts) that I have come to over the years from reading studies and interviews.
1. The difficulty of the revising a resurfacing relates to the cause of the revision. If it is a loose femoral component, then it could be pretty straight forward. If it is due to metalosis that was allowed to progress over time, it could be extremely difficult due to soft tissue destruction. A cup only revision is going to be much easier for an experienced HR surgeon who is used to working around the femoral head and neck, than for a THR surgeon who is used to amputating those out of the way. The one thing that we have plenty of evidence on, is that THR revisions do not have good success rates, which is why people have always been told to wait as long as possible.
2. A common argument against resurfacing it that the larger head requires a larger acetabular component, which cost you acetabular bone stock, which could be a problem in case of revision. Some studies have shown that this may be less of a problem if an experienced surgeon did the primary resurfacing, since they are careful to use the smallest cup possible in order to preserve acetabular bone stock. A recent study from the HSS in New York showed that, given the same native femoral head size, resurfacing patients tended to end up with smaller acetabular cups and therefore less acetabular bone loss, than patients who received large head THRs.
3. It is possible that a THR can have a greater range of motion than an HR. Since the femoral neck has been replaced by a narrower metal junction, the THR can move farther in all directions before impinging on the edge of the cup. This is visually clear, and has been proven in cadaver studies. However, potential range of motion in a THR is not relevant if there is a small head that can dislocate when the range of motion is pushed, unlike an HR.
Once again, these are just my non-medical opinions, but it might show why a person could hear conflicting statements on these topics.