This news is not necessarily new but there have been additional studies into the interaction and it is now considered more dangerous than they originally thought. They have found that Nexium and Prilosec inhibit an enzyme that is important for Plavix to work. There is a list of other medications that are additionally considered to be unsafe with the use of Plavix as well. The problem isn't that the drugs together cause a problem but instead that you don't get the benefit you think you are getting from the Plavix and not having the anti-clotting effect of the Plavix that you think you are getting can be very dangerous if it is needed. 

Although technical, you can read the FDA warning for physicians here:

http://www.fda.gov/Drugs/DrugSafety/PostmarketDrugSafetyInformationforPatientsandProviders/DrugSafetyInformationforHeathcareProfessionals/ucm190787.htm