[davidw]

Both are correct, in a way.

When making template changes, as nexialys stated, you need to modify the templates for all styles.

In what Brandi was talking about this applies to modifications made to vbulletin that are not template related. For example a plugin, product, etc., these will affect all child styles. When the template is within a plugin (usually created by a plugin), then it adds it to all child styles.