What are we objectivists missing?

I have been following (with much amusement) various threads about cables and tweaks where some claim "game changing improvements" and other claim "no difference".  My take is that if you can hear a difference, there must be some difference.  If a device or cable or whatever measures exactly the same it should sound exactly the same.  So what are your opinions on what those differences might be and what are we NOT measuring that would define those differences?