The point of a lot of social research, however, is to point out stuff that people don't find intuitive or even know is happening. The poster at the very top of this thread said something like "actually, I'm much more careful about what I keep from subscription services, versus what I buy in a store." But in fact, there's no real way of knowing this. Survey and self-reporting measures are notoriously bad.
Think of it this way: with chemistry, you know what is the effect of X because you always have a control, where X is not present. That's not possible with social research. When that guy at the very top of this post says "actually, I'm much more careful with what I buy from subscription services," the only way he could know if this is true is if we cloned him -- gave one of them a shirt through a subscription service, the other one would have to find the shirt in a store, and see what happens. We'd then repeat this experiment a hundred times to draw a conclusion.
But since that's obviously impossible, social researchers have to devise clever ways to tease out odd human behavior. In fact, the field from which those studies draw -- behavioral economics -- is all about how people make irrational decisions. The field goes against the idea that we're rational choice actors. So yes, of course the guy at the top of this thread thinks that. He and thousands of other traditional economists would think the same. But behavioral economics is showing that a lot of weird things are happening -- despite what we think we do, what traditional economists think we do, what rational choice theorists think we do, etc.
The blog obviously can't commission a study to do a test with subscription services. It's drawing from a relevant field to say there might be an endowment effect -- and since it's a blog post, not a literature review, it can only lists one or two studies. Adding to this with additional survey research would be odd since people would claim they're being rational, when they're not actually behaving that way. If you asked the students in each of those studies what they thought was happening, they would also say they're acting rationally -- they're keeping the mug or candy bar because they like that thing more. Little do they know that something else is at play.