My informed layman's reading of all this and particularly Chris F. and Glenn C. posts leads me to these two understandings about overtensioning:
1. If the spring material/manufacture is inferior, the spring could be too weak in spring rate or too short from the start, leading to the potential for coil-bind and from there a quick possibilty for overtensioning.
2. If the spring is only "adequate" for the "normal" tensioning and not over engineered to handle the tension required for larger blades and thicker materials and it is constantly used beyond its fatigue point because of this, it will weaken and probably coil-bind leading to the overtensioning again.
So that leads me back to the gist of Mark's orginal position that the guage on the saw is good enough for average use. What I am getting out of all the disussions is that this is probably true as long as the spring in the tensioner is up to design specifications and you are using a blade whose tensioning needs don't exceed the capacity of the tensioning system on the saw.
Does that seem like an accurate summarization of all this?