The defect rate isn't enough to scare me off. I'm pretty sure that if there are any problems, they'll most likely show up early on within the warranty period.
There doesn't seem to be any good explanation as to why so many grado's are showing up defective, but it's not enough to deter me from buying at least one pair. Whatever the issue is, I hope they rectify it sooner rather than later. I don't see what the possible issue could be. Grado has a lot of experience producing 'phones. I really doubt anything has changed drastically in the production/manufacture of the e's.
Perhaps they went with different overseas manufacturers for their parts, but they are supposedly all tested in house before heading out.
The most likely culprit is that QC/final checks are far too cursory, or perhaps even non-existent in a few cases. Or, they are indeed having problems with their suppliers, but it's on them to give each pair a decent final inspection.