Workgroup requires a special client interface to access the vault, but it still allows you to rev control any type of file, not just SW. n my opinion, the Windows Explorer interface in Conisio (Enterprise) is highly overrated, not to say that it's bad, just that it isn't much if any better than having a separate client software interface. They both require learning new stuff.
The main differences are going to be that Enterprise has a real database (which has benefits and detriments), it can do things like workflow for routing ECNs through a sign off loop, and it has multi-site capabilities. And price. They are two completely different products.