I know what you mean Mike.
On the Chalkstreams you are warned to approach with Ninja-like stealth and to stay low etc etc. Sure, the fish (both trout & grayling) will usually flee if they are surprised but they soon return to their lies after 10-15 mins or so. I know this because I am often still there as there always seems to be one fish (usually a big one) that doesn't spook for you to cast at.
We are also told to make you're 1st cast count and if you don't then to walk away. My experience says it is worth casting at a fish as long as he is still there. It is amazing how many times I have covered a fish for 10-15 minutes before he eventually takes the fly...
I used to stay put in one place at Haddo for hours, constantly casting and still caught my fair share of fish at all directions around the boat.
I don't know if there are any hard and fast rules about trout spookiness and I suspect that there are too many variables (water clarity, time of year, food availibility, fishing pressure, etc etc etc) to write a formula. I have always described my own fishing style as "Persistant" or "Relentless" and I find it hard to sit and wait for a fish to reveal itself.
Maybe fisherman are just not patient enough...?
Ewan