I'm afraid neither of these capture E&Z's cryptic point (their lack of detail on this is partly why I asked this question).

A dependent variable is something that is affected by something else (see Chapter 1 for a discussion of this). Thus, saying that "culture is a dep. variable" means that culture is affected by other things, such as the economy, political structure, geography, weather, technology, etc. Their point is that culture is not the "cause" of why society is the way it is; but rather that culture is largely determined by other forces. I call this the "culture as caboose" theory of history, meaning that culture is something that's dragged around by other forces, changing as those forces change.

Since a key component of culture is the values and ideas dominant in a society, this then means that, if correct, values and ideas are NOT key to understanding why a society is structured the way it is. So, for example, we don't have class inequality and a capitalist society because we VALUE"free enterprise" or "individual freedom"; rather, we have social institutions (such as the media, politicians, clergy, teachers, etc) that express support for "free enterprise", etc, BECAUSE we have a capitalist economy, where these ideas promote the interests of the class(es) that benefit from this system.

Jim