This is one response, and I could add that for flying business class it's not the same sort of standing-in-line tedium that the general public is subjected to. But even then, Sam Walton (of Wal-Mart fame) was famous for flying coach, and I doubt anyone questioned his executive productivity.

But I'm not saying corporations shouldn't ever use private jets, just that their use often seems optional rather than a matter of business necessity, which has implications for how such expenses are taxed.