So what's changed about people's memories? Have people become so much more stupid in six years' time? If you want a simple answer for why people use Wikipedia you only need compare the size then and now. People looking for information will go where they can most easily find it.
Nothing has changed about people's memories, what's changed is what people expect from Wikipedia. When we were a new site used only by a handful of geeks, most of which were contributors, nobody cared how reliable we were. That is no longer the case.
We can have a credible encyclopedia without obsessing about it. Your distinction the source and the citation of that source strikes me as more semantic than substantial.
It's necessary to make that distinction in order to point out the flaws in the "let someone else add the sources" arguement.
There seems to be a serious misunderstanding of what "source" means. A source isn't somewhere people can go to verify the fact, it is where the fact came from.
Sounds like a good definition for original research.
What are you talking about? Are you one of these people that doesn't know the difference between "original research" and "research"?
Sometimes a memory can be a reliable source; it just can't be verified.
Only if we know who's memory it is. When it comes to Wikipedia contributors, we rarely know who is doing the editing.
What can be more frustrating than to have been at an event 35 years and know that the citations are dead wrong because they relied on contemporary newspaper clippings from publications that were openly hostile to the event when it happened. This often leaves us with sterile articles that ignore the zeitgeiss of the event. There is a level beyond which the demand for sources becomes counterproductive.
That's frustrating, yes, but if you're allowed to add true details from your memory, what's to stop me adding made up details? Nothing at all. Sources are a requirement for verifiability.