In my opinion they are not. A lot of people won't pick up on differences unless something is pretty off, even if they were intimately familiar with the audio beforehand. Some people are barely able to tell the difference between one and the same piece of music being played to them first in stereo and then in mono. A fundamental problem with blind listening tests, such as those often cited from the venerable Hydrogen Audio forums, is that they provide subjective instead of objective truths - besides everyone's hearing being different, an individual's perception of music also changes by the day as it's affected by their current mood, state of health, emotional state, whether they are rested or not, and so on. Applying a scientific method (e.g. PSNR or spectral analysis) reveals an objective truth of how close a lossy product is to the original, which is where Vorbis has been shown to fall short. But subjectively a lot of users may never notice, nor even care.