I think this is an interesting aside in the article. Seth seems to be arguing that it's the same work, but it really isn't. The amount of money handled does change the difficulty. First, it's going to require more trips to move the money and that is increased labor. More importantly, the risk goes up the more money you're transporting. Maybe those changes are small. OK.
The real difference comes in the value to the firm hiring you. If you're being entrusted with $1M vs $100K, the firm has a greater interest in making sure you're good at your job. Loosing $1M because you hired a poor driver is worse than loosing $100K because you hired a poor driver. Likewise, when we're talking about hiring for a CEO, a firm will want the best since they're entrusting that person with the livelihood of the firm. His or her job may be no more difficult than anyone else's job, but the firm has a high interest in making sure the CEO is competent. An incompetent person in an entry-level position is unlikely to be in a position to do the damage that an incompetent CEO could do to the firm.
So, by paying high salaries, firms hope to be able to take their pick of managers and get the most competent. However, firms have yet to show that they are able to determine the competent from the incompetent. So, at the moment, most firms are simply paying high salaries to whomever is good at politicking and showing themselves in a good light regardless of actual competence.
There is a theory behind it and it's not just marketing. However, the fact that firms have proven unable to filter the competent from the incompetent limits the applicability of that theory.