I love the example Reddit has made with the Digg/Reddit war. Mostly in that it was never a war. I remember hearing their response when they found out about digg was something to the affect of "oh interesting" then continued on.
However, your statement prompted me to do a little research. Here is Alexis' (reddit) story:
"This is a good chance for me to dispel any rumors. We were living in a veil of ignorance for the first month or so at Reddit. We were working our asses off, my co-founder Steve Huffman and I, building a site that we got online, and then two weeks into the site being online we found out that there was this other site called Digg, that had venture funding and it had been out for quite some time."
Source: http://mixergy.com/no-reddit-didnt-copy-digg-heres-how-it-wa...
I've actually started reading Slashdot again in the last year of so, which is funny, because it's growing irrelevance is what drove me to Digg in the first place.
Paul Carr said it best: "So at best they did zero research before they launched Reddit into a space that kinda relies on the founders knowing where to find cool new stuff online."
http://techcrunch.com/2005/06/18/profile-digg/
So is it that absurd that they started on Reddit without knowing about Digg? For that matter, TechCrunch wasn't that popular either in 2005.
He had a captive audience on TechTV (or what was left of it after G4 gutted it) which helped a lot to get the word out and to give it some geek credit.
Then there was a shift from Slashdot (my post never gets shown!) to Digg (my post never gets shown) to Reddit (too many people posting!) now ...Hacker News?
p.s sorry for the drunk post.
Certainly Reddit is quite different but I can see a shift maybe among older users or maybe more of a dual membership.