Did you do a blind test? I cannot for the life of me tell the difference between 256 Kbit/s AAC and a CD in a blind test. (The best equipment I have are 150€ headphones, I tested with them. I did this test to decide whether I should start buying my music online instead of on CDs.)

Tests in which I knew what is what were completely worthless. I nearly always thought that I could tell the difference and that ability magically disappeared in blind tests.

I can tell the difference between 128 KBit/s MP3 and a CD, though.