Hmmm... or is it just more that it might be embarrassing that the actual article sources are not that authoritative? (indeed perhaps just coming from a website!)
Wikipedia's detractors aren't making stuff up out of thin air, often merely drawing on, and exaggerating, the cases where we fail.
I would suggest that in many cases where sources are not cited, it's because they aren't good sources. And this happens all the time on less scrutinised Wikipedia articles.
Doesn't mean it's not plagiarism though to use someone else's work and not accredit it just because it's awkward for you to do so.
But plagiarism is the founding principle of Wikipedia! ;) Okay, not quite. But if there had been strict requirements on using good references in the proper way from the beginning I wonder if the project would ever have gotten off the ground.
Maybe it would have, just a bit more slowly, and be all the better for it. I honestly don't know.
Regards, Haukur