A quote from the link:

"People frequently ask if their 6 volt dymotecs and 6 volt lights can be upgraded to the 12 volt specifications. Unfortunately, this is not possible. Electronic overvoltage protection in all of the 6 volt lights will fail if powered by 12 volts"

Well, duhhh.

Is he that dumb, or does he think we are? Let's make a leap of faith and suppose that a person knows enough to change the bulbs to 12V before running 12 volts to them. What people are asking is what is the internal difference between a 6V and 12V dynamo, and can the 12V components be retrofitted?

Beyond that, I'm mystified as to why a 12V dynamo should cost twice as much as a 6V (don't tell me they charge by the volt...); the cost of materials couldn't be very much different, and I don't think amortizing over a smaller production run quite covers it either.