How is it not Blizzard's fault? They designed an UI where this happens A LOT. It's kind of like putting a "sell all gear" button and just asking players not to accidentally click on it. Any designer (UI, product, etc.) will tell you how much fail this is on multiple levels. I am in awe that people will defend Blizzard's lazy coding.
1) I'm not defending their coding. It's just never even struck me as an issue.
2) How it is not Blizzard's fault? That's easy. You're the one that equipped gear you didn't mean to, and then sold your good gear.
3) A sell all gear button comparison is ridiculous. A better comparison would be driving your BMW to a Ford dealership to test drive a used Focus, and then leaving in the focus without noticing it.