The tab is not new and Open Source downloads have been available for many years, you probably just hadn't notice it before now! 
As an example, the VMware-ws902-open-source.tgz file is not a Open Source installer like the normal installer VMware-workstation-full-9.0.2-1031769.exe file is and is instead a collection of Open Source programs that VMware may in some manner utilize in is proprietary finished product.