Why center the information? To get it accurately centered you have to count letters, divide by two, and add it to the number of spaces available. A pain in the rear. And for what purpose? Especially since Obama’s is the ONLY time anybody ever did it that way. That is the point that is being made, and it is a very valid point. It’s an anomaly for very possibly the same typist who typed the Nordyke BC’s to not just use the left-hand margin and tabs.
Centering the information in this case does not mean centering it mathematically (which actually would be impossible unless the forms were specifically drawn-up in accordance with the typewriter that was going to be used). Centering here means eyeballing it, which is clearly how this particular form was filled out. Not any more of a pain than any other way of filling out the form. As for the fact that Obama's is the only one out of four examples (that I've seen, all from different years except the Nordyke - where, it should be noted, the street address is centered, not left-justified) doesn't mean much at all, statistically or otherwise.