Because [`fs.exists()`](https://nodejs.org/api/fs.html#fs_fs_exists_path_callback) is being [deprecated](https://github.com/iojs/io.js/issues/103), but there's still a genuine use-case of being able to check if a path exists for other purposes than doing IO with it.
> In particular, checking if a file exists before opening it is an anti-pattern that leaves you vulnerable to race conditions: another process may remove the file between the calls to `fs.exists()` and `fs.open()`. Just open the file and handle the error when it's not there.