I don't doubt it exists in some cases, but if it were as ubiquitous as many say, I'd suspect to find evidence of other conspiracies. Many other industries also lack a centralized organization (one ostensibly for standardization) to facilitate such a conspiracy. Overall I just find the argument very weak, especially in the face of normal market forces and cost-competition being sufficient to explain much of the observed changes.
I do agree that appliances likely represent a real decline in durability over the past couple decades.