I think what is being asked here is why after entering the login credentials does the user have to be put onto an other page saying that the password or username is incorrect.
I would say that many sites do this but many also check the info from one page using JQuery or/and AJAX libraries and put out an error message like for example phpMyAdmin does this check without page reloading.
Maybe this is one of those sites which doesn't have such thing yet, it would be interesting to see it implemented as it would cause less frustrations when getting the login incorrect and all of that stuff.