Drupal must have a special attention with information which deal with user's identity.
A login is just a short word to sign in faster. The username can be short also but is a different thing than a login because it identify the user for other people. In drupal account editing page, login and username are both the same for now but they should not.
Picture, username and signature are three identity datas that should appear and be managable on a different page than other settings.
There is a module http://drupal.org/project/alt_login
Unfortunately it doesnt adress this issue.
The solution will be :
1 ) To let user login with their email adress or with their login (admin should be able to choose which one is required during inscription but it seems that email is always needed, so login should be optional or not)
2) To ask user define a username if they want to create content.