I discovered the ABX tester for Foobar yesterday and spend the better part of the day playing with it. I was surprised that all three of my headphones (see sig below) were able to discern between lossy and lossless, but only on some albums. On other albums I could not tell a difference.
But for the albums I could discern the difference the difference was obvious on all of my headphones, which leads me to believe that lossless is really only necessary for albums that are extremely well produced. Most albums do not have a high enough production quality to warrant lossless playback. This makes sense because a lot of my music is made by independent artists (I listen to a LOT of underground music).
So, it seems to really come down to production quality, not entirely fidelity of the headphones. All of the headphones were "hi-fi" enough. Not all of the albums were.
Anybody else notice this? The abX tester is a great tool, I was really surprised at how good the quality of V0 mp3 tracks is.