Choosing Between SQL Server 2008 R2 and SQL Server 2012 - Which to learn about first?
Yes, The certification exams for 2008 R2 are retired, but you can start learning 2008 R2 and once you master the concepts, move to the new 2012 features.

Even if your company (current) has no upgrade plans, your future company may already have upgraded all their servers to SQL Server 2012. 

Check out What's new in SQL Server 2012. Also check Top 5 SQL Server 2012 Features by Aaron Bertrand.