This is vital to what makes a good leader. But at the same time, it must be balanced with toughness. A leader shouldn't be polite out of weakness of fear. They should be polite for the purpose of uniting the team. If the leader does this in a balanced way (is kind and polite, yet tough and authoritative), this would be a good characteristic.

No, a leader needs to be tough...to step on a few people's toes if necessary.

Kind and polite is nice, and if we're rating salespeople and receptionists it would rank high, but I don't know about it being a major part of being a leader. A person that is overly kind and polite can easily be taken advantage of if in a position of authority.