When he says 'interface element', do you take that to mean a button or what? In one sense, everything on the screen is an 'interface element' ...
Now that I think about it, I stick to CSS most of the time and try to keep images to a minimum (front-end optimization is a tough habit to kick), so I may forget this by the time the next occasion arises.
Given that these elements are only eye candy, I don't worry too much that they are invisible on IE and older browsers. Think of it as free candy.
We developers might dismiss 1px drop shadows an unimportant; after all, the "real" application is the code we write. But users make no such distinctions. To them, the interface is the application.