It’s possible to use one high-resolution icon for all devices. Devices with smaller screens or lower display resolutions automatically resize the icon. If no icons are specified in the HTML, iOS will search the website’s root directory for icons with the apple-touch-icon or apple-touch-icon-precomposed prefix.
So if you do not include this icon at all, you can get such error message in web log file: ‘The controller for path ‘/apple-touch-icon.png’ could not be found’.
What you should do to fix that is create and add those images (I produce apple-touch-icon.png and apple-touch-icon-precomposed.png, 180*180 px, usually). This will improve your user experience also – if a user added your website on his home screen, he got your nice predefined icon (a thumbnail screenshot of the page will be used, if you haven’t provided a custom touch icon).