h5bp/html5-boilerplate — comment on commit 0bf9143cd135df0b0357d4c7c50dcdb91dd85724
File: 404.html line 30
By necolas:

It's not correct to say that using an ID is simply "the right thing". The ID attribute is only there to allow you to set a unique identifier on an element - http://dev.w3.org/html5/spec/Overview.html#the-id-attribute - and most modern development practices shy from styling elements based on their ID - http://oli.jp/2011/ids/ ...so it's staying as a class.