One of the cafe regulars, again clearly a sensor (you should see the guy's apartment; how ornate it is), perhaps an ISTJ, had heard of the MBTI. And when I explained my type, he said, yes, that was him too. Mm-hmm, I thought. Moving right along. Generally an astute guy, though any kind of conversation with him slams against that S/N communication divide.
In my experience, it's always a "me too" thing. I think there's a huge horoscope effect going on here, along with a need for belonging and identification. You know how horoscopes are written so generally that anyone can find applicable details, then mentally skew a description so it feels like it was specifically tailored to that person. This isn't a critical process, and it doesn't come from a place of acute self-awareness; rather it comes from a desire to see one's self reflected. Combine that with a sense of peer pressure -- well, my friend says this describes him, and if he's my friend we can't be that different -- and I guess it shouldn't come as much of a surprise.
The thing is, the MBTI does describe a certain spectrum. All of us display all of the behaviors of every type at some point in our lives, under certain circumstances. It's just that with each of us, some of the colors are bolder than others. So (to resort to stereotype about sensors, but applied to these particular case studies) if you're not as comfortable with introspecting and filtering that information and abstracting some broad tendencies about yourself, and you're not very interested in the theory for its own sake, I can see it being harder to sort through the noise and figure out what actually applies to you.
Short version: I think the people described here are looking at the system for something other than abstract understanding. It seems to be mostly social validation.