Giselle Abramovich offers some insights into the simplicity of Responsive Design, or at least the appearance of simplicity, and calls it a myth.
Responsive design certainly has its challenges. For example, it will hide content on small screens, but the content still needs to be downloaded, and this causes performance issues on mobile phones. Load times could be long. Other less attractive characteristics of responsive design include time constraints; it takes a longer time to create Web pages, and they need new content-management workflows.