Of course it's also a case of the culture within a specific nation as well, I wont disagree with you on that.
Regarding the number of positive tests. I found some statistics on WADAs homepage. I picked a few different sports, the numbers represent numberofTests, numberofPositives, percentage. Please bear in mind that the statistics represent the sports on any level - no just the top level athletes.
Athletics: 23 305 - 304 - 1,30 %
Cycling: 16 462 - 643 - 3,91 %
Ice Hockey: 4385 - 104 - 2,37 %
Skiing: 3 844 - 71 - 1,85 %
Wightlifting: 6 620 - 200 - 3,09 %
I have only look at it for a couple of minutes, so there is probably a lot of information I haven't taken account of. Here's the link:
http://www.wada-ama.org/rtecontent/document/LABSTATS_2007.PDF
Regarding your last comment; I believe Bjørn Dæhlie was better than the rest because of three things:
1. He did an amazing amount of training
2. The Norwegian Ski Federations used millions of NOK to develop technology, for example waxing(?) methods (not sure about the english term)
3. He had an extremly focused mind.
Edit: And again, I can second ingsve's post.