You are correct on both accounts. Network drives are not listed by default, but they can be resolved by drive letter in the "Path". I can see two reasons for this:
1. Simplicity. We create a much cleaner look by not showing all mounted drives/devices by default. This may not be the best reason but then again, I'm just guessing.
2. Best Practices. Looking back at how QV Server works, when running a reload through the QVS it cannot resolve mounted network drives by drive letters as it's being ran as a "service" and not a "user". To that end we recommend people use UNC paths as much as possible. So, by not showing the mounted drives by default we don't encourage people to follow a direction that wouldn't be best practices. Too many negatives in one sentence? Maybe.
Thanks for bring this up. If from online help menu Creating a new folder data connection
It has mentioned you can Type in the UNC path to connect data on network drive.
But I would agree with you this might not so detail why this mount drives can't be selected from the dialog box. I will bring this back to our internal discussion see if we can improve this in the future. Cheers!