Is it possible that some of the differences shown in this page come from phase changes rather than attenuation? If so, is such a phase change perceptible, even in principle?
Yes, the difference signal is present in both the residue and the mp3, not lost just shifted in phase so it doesn't cancel exactly any more. In general the phase shifts are not audible but you can construct some signals (like two impulses very close together) that fool MP3 so the encoded signal has the correct spectrum but the wrong phase to reconstruct the impulses so sounds different.
