I've been thinking about about various psych study findings:

• people who feel lucky and/or are happy tend to be more successful
• people who are more successful tend to be more emotionally/tonally dominant in conversation (at least with men, I think the findings were different with women)
• depressed people are more sensitive to other people's emotions

Since depressed people are by nature not feeling too happy or lucky, and therefore on average going to be less successful, perhaps they are more focused on reading other people's emotions because they are more likely to be adjusting their emotional tone to fit that of others.