About follow-up studies - I think you mean that people are going to hurt their backs anyway so why produce evidence to support an argument that physio won't prevent future occurrences, right?
No, I am simply saying that in longterm followups of placebo and treatments groups both will exhibit similar results for low back pain, say at 12 months, 18 months or 2 years. Luckily this is as the majority will be pretty much pain free. This is as the majority of LBP is non-specific and therefore those that will still be suffering in a placebo group will be to small to exhibit any statistical significance.

We should focus our attention on the short term recovery and put a measure/cost against that to show how effective we can be. To continue to look at longterm measures will siply continue to weaken our position on why physio should be the first port of call for a client with LBP.