Good summary. This is also convenient from the perspective of not having to try to convene, organize, etc. a shareholder vote. For many years, a lot took place just on the say-so of the board/CEO. Makes sense given how expensive it is to have proxy voting w/ nearly 5b shares outstanding and not enough scratch to put a drill in the ground! So not casting blame, just making note.  

Also, bear in mind that, as Directors, P & B still have fiduciary duties to ALL shareholders. So if they were to exercise these super-voting shares in a manner that unduly benefitted themselves at the expense of the other shareholders, they could be sued. And if the money at stake is big enough, you will find more than enough lawyers willing to take on that shareholders derivative suit. So there are guardrails here...