I have two different opinions for this issue, besides what everybody has already said. One thing is that 930s are made in many places alround the world, and this issue appears in 930s from many different places. Mine is from Brazil, and I read that pones from Europe, HK, etc have the same problema. Could it be possible that mics are made by the same provider and after the update the failed mics blew away? it's strange...
And second, and more important, I could suggest an easy solution to MS: give us a simple software fix that redirects the mic that captures the audio for speaker mode to any other of the FOUR mics this phone has!!! Is it so difficult to do that? maybe it is as simple as a registry edit... Think that Camera mode records audio because it is using 4 mics at a time, at least 3 are recording and it works... I would be definitely happy with a solution like that...