“Nothing comes even remotely close in sound quality.” — Mumble?
Ventrilo and Mumble do have far superior support for massive number of people in a chat room. If you're participating in large MMO raids or Eve Online type festivities the Skype doesn't have the necessary features. For my ~5 player parties Skype blows everything else out of the water and isn't even close.
The two codecs have been merged/improved into Opus, which is one of the mandatory audio codecs for WebRTC.
But all three are moving to Opus, so very soon it's not going to be the codec itself that will differentiate audio quality between them.
It's also secure, FOSS, cross-platform, and implements a consistent UI. Skype has none of these.