One of the biggest changes affecting marshals was the way so many circuits were re-profiled in one year to make the most dangerous corners a little bit safer. Bigger run offs, bigger gravel traps, more catch fencing, bigger tyre walls with conveyor belts on the front etc. That went hand in hand with modification to make F1 cars slower and safer.
Around this time that the extractable F1 seat was developed
http://composite.about.com/library/P.../bljaguar1.htm
Wasn't the biggest change, the change in culture, that there shouldn't literally be immovable obstacles in the pursuit of better safety. Many corners where for decades it was said you can't move that to make it safer, suddenly it wasn't as big a problem to change it. Suppose its what Dave Brailsford calls the 'aggregation of marginal gains', improve everything a little to make a step foward in safety.