In the section explaining use of a directory and multiple files for a plugin, an example is provided that suggests the directory name and "main file" name should be the same. If so, perhaps this should be explicitly noted?
Many well regarded plugins, authored by experienced WordPress developers still use the constants - they seem to have missed this memo: http://codex.wordpress.org/Determining_Plugin_and_Content_Directories -- it doesn't help that the introduction to writing a plugin is also out of date.