Strad, I don't get what got you pissed.
I'm 38, been watching F1 since the early 80s, reading any magazine I could find before internet appeared, including old magazines from the 50s, 60s and 70s, listened to older F1 fans etc.
I've heard and read about some that you've mentioned like Gilles, Bandini, Peterson, Clark, Cevert... If you haven't noticed most of them were very successful drivers, one champion among mentioned and several race winners.
Purley had no fame but this heroic act, and neither did poor Williamson, so they were never mentioned in historical texts together with majority of those you've mentioned.
Williamson's death is not as "in" as Cevert's for some reason. Just checked wikipedia 1973 season, the only death it mentions is Cevert's!
http://en.wikipedia.org/wiki/1973_Formula_One_season
With no disrespect to Cevert, I'd dare to say that repeated fact that Purley was the only man on the track that day among famous or famous to become drivers like Stewart, Beltoise, Hunt, Pace, Regazzoni, Peterson, Hill, Lauda, Hulme and Amon (including Cevert) who didn't stop to help Williamson, pushed Purley's heroic act at the bottom of F1 history drawer - not to raise any dust of unpleasant questions that might dim the glow of some champions and OBEs fame.
For instance, check famous
http://www.schlegelmilch.com historical photo archive. Purley or Williamson aren't even listed, not a single photo of those two.
Why? Why are there other drivers from 1973 but not those two?
Was Williamson's death lesser tragedy than Cevert's, only because Cevert was more successful and drove for the top team?
No one knows everything, and person learns as long as he lives. Therefore, I see no reason for your underrating of forum members who have never heard about this incident that happened almost 40 years ago.
As you can see, the blame is not on those who read history, but on those who write it.