There are some key differences. Examples:
You can see all of the VCs for an image in Grid view (i.e., side by side). So you could, for instance, see a color rendition and a B&W rendition (a virtual copy) side by side in Grid View. If a master image has 10 virtual copies you could see all 11 renditions (master + 10 VCs) all side by side. This also means you could select all 11 versions and print them in batch. You cannot do any of this with snapshots.
Snapshots are saved as part of the image XMP and can be shared with Camera Raw. For example, if for a given image you create 3 snapshots, save the metadata to the file (sidecar XMP) and then load the file in Camera Raw plug-in, you'll see the same 3 snapshots in CR plug-in. You cannot do this with VCs, which are internal to LR only.