Semantics in play here. Graded in the auction world means a numerical grade has been established and documented on a cert. No cert, no numerical grade. Fine, VF, XF and Superb are thrown around liberally but are as always very subjective.
While I understand that for some issues certificates are a must, I collect stamps and not certificates. The fun of our hobby is trying to find 'the' stamp in near perfect condition in a mixture or a collection.
Numerical grading is almost exclusively limited to US stamps it seems. I've seen a few Canadian graded stamps, but not common.
And VF etc are definitely subjective & useless in descriptions - there's one active online vendor I know of that lists every single stamp they have for sale as "No Faults Extra Fine!", even if the stamp looks like it was coughed up by my dog.
Grading and certification are two subjects. Whereas I get the impression North American certificates include a grade, European certificates rarely do so. In Europe the closest thing to grading is the distinction between good, very fine and superb (or some local variety). And that type of description is not uniformly applied. It, rarely, is mentioned on a certificate. And superb or very fine does not imply the item comes with a certificate.
I cannot say how things are "down under," in Asia, nor in Latin America.
For me, I am more interested in having an expert opinion regarding repairs, reperforations, regumming, etc. If I am spending 100's or 1000's of dollars on something I would like to have an expert, using high end equipment, to verify a stamp has not been altered. I have followed many of posts on this site regarding reperforations and have come to the conclusion that many reperf jobs are scary good. It's nice to have a certificate stating an opinion that a stamp is free of faults.
PSE grading doesn't mean anything to me personally ... I can use my own eye for centering, depth of color, impression (the things that draw me a stamp anyway). That's why I use PF basically for verifying soundness. I see PSE as mainly a grading operation. When I see common stamps from the 30's 40's with PSE grades of 98 getting > $100 I shake my head. But there must be buyers out there to push prices up to that level. To each his own ...