[vladms]

> I think we seek to credit the source for reasons that are not clear.

For me a source means I can verify some claims, find another opinion/presentation, are able to view other work based on that source.

It is the difference between having links between web pages or having only independent web pages. I guess we can all agree there is value in having the information "X was based on Y".

The reason people do not credit can also be that they don't add any value. If the original source is more complete, more correct and better presented then they might "loose" their perceived value. Does this happen in all cases? Probably not. But it is my first instinct when I see it (happens a lot to "news" article as well for example, when talking about papers, university announcements, etc, things that could be easily "linked")