Matt’s got it right. DSC consists of layers; the DSC functionality itself, plus “resources” that actually check and do stuff. We don’t have a lot of resources yet.
Over time, expect to see (I personally believe) SCCM incorporate DSC in lieu of its own configuration auditing functionality. Over time, (I and others think) expect DSC to start to replace GPO. Right now we’re in a period where the core functionality exists, but it doesn’t do much. As product teams start writing on top of DSC – just as they eventually did with PowerShell itself – it becomes more useful.
You didn’t mention the functional overlap between DSC and SCVMM, but there’s a lot there also. Again, over time, SCVMM will continue to do what it does – but it’ll do it by using DSC, instead of its current implementation.