One change for ConfigMgr 2012 is that Secondary Sites now require a version of SQL Sever running on them. Why? Due to the way ConfigMgr 2012 now utilizes SQL replication instead of of file replication (in most instances), an instance of SQL Server is required so that it can continue to report to the parent primary site. Having SQL Server on the Secondary site also bumps up the supported number of clients for the server. See: ConfigMgr 2012 sounds neat, but can it scale?
Does this mean you’ll need to install SQL Server manually on each Secondary site? No. While you can if you desire full SQL functionality and optimum license seats on the box, when you install the Secondary site, setup automatically installs SQL Server Express if SQL Server is not already installed.