No it's not compulsory, but if you want to use Outlook to see what your friends are doing on Facebook, you can with Outlook 2013.
While Microsoft has provided 'Social Connectors' to integrate Outlook 2010 with services such as Facebook and LinkedIn, this feature is going to be part of Outlook 2013.
A new post to Microsoft's Outlook Blog explains that information from your accounts on Facebook and LinkedIn can be made available to the Office suite by entering your usernames and passwords for those services in the Social Network Accounts section of Account Settings.
Then when you display a Contact Card, it will show information drawn from Facebook and LinkedIn for that person, subject to their privacy settings. The information available includes pictures and recent activity.
Contact Cards are available in various contexts within Office 2013, including Word comments, Lync contacts, and Outlook email recipients. Social network information appears in the What's New tab.
Outlook 2013 also presents Contact Cards from its People view.
The release date and Australian pricing for Office 2013 has yet to be announced, but we do know customers will need to choose between a conventional perpetual licence and an annual rental.