It has always struck me as odd, given that Opus' config backup files are actually zip files, that .ocb is not included by default in the zip file type list. When a new stable release comes out I routinely backup my live config then uninstall and reinstall Opus in order in order to capture, examine and backup the current set of baseline defaults. A "vanilla" config is invaluable for testing purposes but almost inevitably the first thing I want to do after loading a baseline is to extract a test script from a config backup (.ocb) of my live system. Double clicking on the .ocb to open it doesn't work until I add the .ocb extension. Catches me every time. 
While you can look inside of an ocb backup, that isn't the primary purpose of them, and you can break the ability to restore the backup by messing around inside the archive.
So it's an option but it isn't a default.
If you want a config backup for extracting individual files, just zip your config folder normally instead.
A virtual machine is a better way to keep a vanilla config for testing than resetting your real config every update. That's what we use.
I do this in a VM. Accessing ocb files is purely for retrieving things like scripts, buttons, toolbars, filters, etc..