Alice,
I am certainly not qualified to give a lecture on the chemistry of the different resins and celluloids. The old, classic Italian resins and celluloids are truly beautiful in my opinion. Whether or not people are counting on the name to give perceived value for newer products is certainly open to debate.
Spend some time with Google and research the subject. I think you will see some amazing pens that I would love to have access to the blanks used.
FWIW,