In other words, the importance of PR given by Google in SERP changes with different countries.
I find the whole discussion of Pagerank difficult. To me, Pagerank is an "external indication", not a "ranking factor" itself. Pagerank is based on the authority of the website in question which is based on the authority of the websites linking to it.
That is THEN given a numerical badge of honour.
Pagerank (the number) means nothing in relation to ranking. Authorative backlinks are simply huge in affecting ranking, however. If we're talking about the authorative backlinks that Pagerank is based on, then that not only matters, it is the single most important thing you can do.
The number is so unimportant: e.g. pages drop Pagerank all the time from 6 to 5 or 4 to 3 simply because the number of web pages used in the algorithm has increased dramatically. The SERPS are totally unaffected by such a drop in Pagerank.
For me, it is a hell of a good way to diagnose my own pages, crawler access, link flow, and etc.