Yes. Some (most) Ventrilo servers are configured for the GSM codec which is not currently supported by the Mac version of Ventrilo. Administrators of such servers are usually reluctant to change the codec to the SPEEX codec which is currently supported for the Mac version. This is why we have to use the Windows version of Ventrilo.
Yes, it would be a lot easier if Flagship would support the GSM codec. There is still no ETA on that happening. Until then, this is our option.