On February 25, 2014 Microsoft released Exchange 2013 SP1, an interesting upgrade in the Exchange 2013 program. Besides SP1 new UM Language Packs have been released as well. For more detailed information please check the SP1 release notes. At the same time Microsoft has released Update Rollup 5 for Exchange 2010 SP3 and Update Rollup 13 for Exchange 2007 SP3.
Looking at the Cumulative Updates with Exchange 2013, SP1 is identical to CU4. One reason for releasing a Service Packs is the support lifecycle. Major releases and Service Packs of a Microsoft product are included in the support lifecycle, Cumulative Updates are not.