The OpenGlobal VirtueMart Downloadable Products extension is released under a GPL licence so you can do whatever you want with it. The "core" equivalent is released under a proprietary licence which I have been unable to find.
Also, just as a matter of principle, a lot of people have issues with the idea of the core team removing "free" functionality from a product so that you can sell it. For this reason, the "core" equivalent has a bit of a stigma attached to it.
The OpenGlobal extension was produced for our own use (as our name suggests, we use open source and open licences wherever possible and avoid proprietary licences) and we released it for anyone with similar values.
I assume the functionality is largely the same but as we cannot legally accept a proprietary licence we cannot read, we've been unable to download it.