I want to believe that most of us don't do it intentionally. It just comes out of happiness for those who tried and triumphed. I ask for forgiveness from those I may have hurt but it was unintentional. The truth is, I catch myself wondering at every lesson whether I paid more attention to certain students than to others.
When you become an honour student it is such a big deal that you (teacher) feel it is a natural consequence to congratulate that student and ask him/her for his/her advice in order to help others.
Of course, that does not mean we (the teachers) should neglect others. Each person is unique and functions differently. We are all obliged to remember and respect that. Besides paying too much attention to the people who don't need it that much is uneducational.