Hmm, I would think salary would be one of the smaller considerations when choosing a CEO at that level. It's generally going to be a drop in the budget compared to annual revenue. A negotiation point for sure, but more of a side show to other concerns.
Then it's even less important. When you need Superman to save the world, you don't quibble over his price. Okay, maybe a little, but everybody's a professional here.
Just because a company is worth billions doesn't mean they are willing to throw away millions. There are still lawyers out there looking to bring derivative actions.
The corporate boards members tend to be CEOs of other companies so they have a tendency to give each other raises because it is in their best interest.
It was explained to me this way: in the US executive boards are unevenly weighted toward CO interests. In countries where wage experts and workers are more likely to sit on boards the ratio isn't absurd because boards are less likely to vote for higher executive wages (Japan and Europe have reasonable CEO wages).
In Japan at least a large fraction of the compensation comes in non-monetary "perks". Ex: Company car, use of company plane, etc. Similar things happen in Europe.
Though I'm sure it isn't as insane as it is in the US.