"But people buy expensive receivers because they sound better than cheaper receivers."

Modify the above to read: "people buy expensive recievers because they think they sound better", and I might agree. :-) Their are also details like fit & finish, pride in having the 'top of the line', etc. Some hi-end recievers have featues that others don't. Some recievers have audible noise problems-i've acutally heard this in hi and low end recievers. Of course, I don't think units that demonstrate audible noise(hiss, rf, etc.) problems are worth a hoot, personally. :-)

"And yet these same people question that integrateds and separates which use much better parts, don't suffer the interference, etc don't? If people are not hearing the difference then they have a problem with the room and or the speakers."

If they don't hear a difference, it could just be that their are NO differences that are audible. Now, I will state that things may often SEEM to sound different when their is no true audible difference, but their is more than just true audible factors at play here(read, pyschological).

-Chris