Service Pack *TWO* for SQL Server 2008 R2 was released in July 2012. Lifecycles for service packs for server applications are one year, which means that support for Service Pack 1 installations expired in July, 2013. Personally I'd suggest not worrying about this two year old security update, but rather install the current Service Pack on your database instances.(There were also several Cumulative Updates, not available via WSUS, that apply to this version as well.)
The core build of SQL2008R2SP1 is 10.50.2500 (Jun 17 2011). Your image shows build 2550 as installed. Checking a reference of all known SQL Server builds, we'll find that 10.50.2550 is the build number including MS12-070.
So, the reason this update is reported as NotApplicable is because it's already included in the installed instance.