The Messages is a messaging experience, and email is just one part of it. Seems like that high-school students think of email as too formal.
But in the case of Facebook messaging they don't need to add email and title every time. It also collects all of your conversation with each person in one - including chat, SMS, IMs, email – so it makes social networking even more easier.
Link: http://www.facebook.com/messages/
Messages are not grouped by date or subject line, they are sorted into one ongoing conversation with each friend or group. The Social Inbox sorts your messages from friends you are close with and you have a separate folder for those that you are not interested in, so you decide whose messages you want to see.
If you don't want to sign in to your email account and spend time with typing email address and try to find out the title of your letter, Facebook Messages is for you! You can get in touch with your friends in seconds and several ways.
The newest key features of Messages are: faster interaction, integrated communication, smart filtering, revamped search, group conversations, forwarding and sending attachments.