It's not clear that the results of 23andMe where much better than chance:
It is, actually, quite clear. Chance doesn't have much to do with different weightings and different baselines. Your link, e.g., says:
The Venter study notes that, in some cases, companies define the average population disease risk differently. “Navigenics distinguishes population disease risk between men and women (for example, men are more likely to have heart attacks than women), whereas 23andMe primarily takes into account age (for example, incidence of rheumatoid arthritis increases with age),”
Also, have you looked at studies examining how much different doctors agree with each other about same patients? Hint: not much. Here is one such study.
Also, have you looked at studies examining how much different doctors agree with each other about same patients
But they're a powerful entrenched interest, therefore their mistakes are a-ok.
I used to work for a company that made a machine that scanned pap smear slides for cancer, so I saw some of the data you describe.
In this case, the problem wasn't as much in the inter observer rates as the false negative rates. A significant fraction of slides with abnormalities, as detected by exhaustive examination by experts, were missed by the large commercial ...
This is prompted by Scott's excellent article, Meditations on Moloch.
I might caricature (grossly unfairly) his post like this: