In general, just calculate the loads on a blade tip to see why fancy mechanisms don't stand a chance - the tip of a typical helo blade has between 600 and 1000 g's on it due to CF. That means a 1 oz flap is exerting about 60 pounds of whirling force on its tracks and hinges. Only for a few seconds, until it flys off, of course.
Wood is an excellent medium for low load work, but the inherent strength is very very low relative to metals. By inherent strength, I mean pounds per square inch. A wood beam must be much deeper to hold the load, so it becomes very hard to package as the loads go up, but the blade wants to be thin. Look again at that film "rotor.avi" to imagine what wood would do under the higher speed environment. Development of aluminum spar blades was one of the technological leaps for helos, allowing Vne to jump to 150 knots instead of the 100 or so prior. Blade motions and stresses at speed are not able to be handled by wood.
Here is a good discussion, note that aluminum is 10 times stronger than wood:
http://en.wikipedia.org/wiki/Tensile_strength
Some more complete strength data:
http://www.efunda.com/materials/comm...anicalStrength
Regarding swapping heads on a helo, it is not very simple. Imagine buying a set of racing tires and putting them on your Chevy Vega. Cut the wheel once and watch the front end come off. The entire helo is designed as a unit, with each connecting piece optimized for the loads it gets from its neighbor.
For a direct illustration of this, look at the mess the US Marines created when they decided to swap the 2 bladed Cobra head for a 4 bladed soft inplane rotor. They ended up redesigning the entire fuselage to chase the cracks they were getting from the higher loads of the new head. Actually, Bell was chasing these cracks, and paid handsomely for the effort. Nobody ever took out the Bell salesmen/engineers who sold this nightmare to the USMC and spanked them for their mistakes, I am sure. After all, they then turned around and sold the Yankee and Zulu, with similar development nightmares!