A bit more about why the study in the OP was retracted.
The study would not have passed an ethics board because the author, El Azab, did not get consent from the JW control group. How he set this study up was to mine data on historic cases of JW patients and then compare that fabricated 'control group' to another group of patients.
This is not ethical. The patients did not consent to their information being published. Even if their identifying information had been removed, ethical standards in research would be breached.
For more info on this, concerning a different case of retraction (not JW or blood related): http://retractionwatch.com/2016/06/30/patients-did-not-okay-publishing-brain-surgery-details/
I wonder how many more medical studies exist, in the journals to date and in the 'dead' archives...the studies not published, where JW patients have not given consent for their medical information to be used for research purposes...where their medical data has been mined in order to promote noblood alternative treatments. It wouldn't surprise me if this has happened many, many times