I can't comment on the idea of "typical" but I do think there are a lot of houses everywhere that aren't completely sheathed. I would be willing to bet on that. I admit having helped build one that was sheathed on the corners and fitted with pink foam board on all 4 sides. The sheathing keeps the house from falling over, and that 4" extra, in a separate piece, can't help you. You may disagree with this, but it's not about you. It's about what the guy building the house thought. I'm going to bet he thought sheathing keeps the house from falling over.
A lot of people who live where electricity is cheap and the temperature is moderate cared very little about insulation and vapor barriers and all that. I would go so far as to say inattention to detail with regards to insulation is actually typical. The people building the house, if they didn't live in it, the cost of heating it had no impact on them at all. Obviously there are vast areas where nobody cared. People may believe that there was some sort of "insulation inspector" somewhere, but that's not how it is.
P.S. It sounds like there might be some beliefs about what sheathing is and what it does that need to be defended in this thread. You know what I mean? Like "if this sheathing doesn't go all the way to the top, then the house isn't [something]" Is this actually true?