The Creative Commons license that the Fugue icon set is under says, "You must attribute the work in the manner specified by the author or licensor," yet none is

The Creative Commons license that the Fugue icon set is under says, "You must attribute the work in the manner specified by the author or licensor," yet none is specified. In addition, purchasing a license for the Fugue set is listed at $50/user. How does this work in terms of web apps?