Yixin,
I'm really not an expert in this area at all, but have gleaned bits of insight from an agronomist friend in Matera and reading here and there. I don't understand the mechanisms, or have enough info to compare sites and results in a meaningful way.
In an effort to answer question more directly, I have no idea how much rootstock plays into all of this. I don't know which rootstocks are commonly used where, or whether they might share common characteristics. There are rootstock guides, such as
http://www.californiagrapevine.com/images/Chart 2.pdf that can be referenced, and maybe that could lead to better understanding.
Using the examples we've already discussed here, one could ask do the predominant rootstocks used in Oregon Jory sites share the same characteristics as the rootstocks used in the Vulture area? As those on Etna?
Does Oregon pinot even show that characteristic "volcanic quality" that Oliver is talking about? What about paleosoils? It's complex stuff that I've not had the chutzpah to get into seriously, being content to drink great wines as I am!
One thing that I've kind of been using as a quiet, but working, hypothesis is that friable, fertile volcanic soils allow deep, complex, root system development, which works along the lines of the old vine thing, i.e. that old vines produce more characterful fruit. Do old vines also have more complex root systems? It stands to reason, no?
Lots of questions, few answers (from me, anyway)!