- The content is readable by most people without having to have specialized knowledge on the subject.
- The content is open and reviewed by multiple people.
- You have links to the references. In this case there is a link to this NIH article. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2667526/ But the content is more technical and harder to read for most people.
I can provide plenty of UK links which refer to Down's syndrome.
By the way, I try to light a candle as well as curse the darkness at Wikipedia, by gathering lists of good sources for all the Wikipedians to use,
https://en.wikipedia.org/wiki/User:WeijiBaikeBianji/Intellig...
https://en.wikipedia.org/wiki/User:WeijiBaikeBianji/Anthropo...
and by updating articles that have long been tagged as needing improvement.
https://en.wikipedia.org/wiki/IQ_classification
I wish that Wikipedia were much better, but the current way to make it better is for people to roll up their sleeves and do something about making it better.