If you're point was that it is unlikely that one would go immediately from poverty to the Presidency, then you are quite right.
Of course, this most likely has to do with the fact that both political parties, and the American people, expect their president (and the proverbial leader of the free world) to have at least SOME qualifying experience to get elected, be it political, military or the like. Such exerience does not, of course, typically lend itself to poverty.
On the other hand, if your point is that, by the time a Person is President, he or she is de facto some sort of blue blood, I would respectfully disagree.
The fact that one might have been born a "commoner" and then rose, Horatiao-Alge style, from the depths of that commonality to high office does not mean that he has forgotten his roots.
To use, again, the most recent example of Clinton, by all accounts Clinton was quite common in his tastes (no Hillary or Monica jokes, please). His favorite food was things like hamburgers, he listened to Elvis Presley and his last car was a Chevy.
I think, perhaps, in reading your post, you are defining "commoner" too narrowly.
