Why is it so easy to tell the difference between live and recorded music?

I guess I should explain why wide even sound dispersion is critical. Maybe Steve will read this and learn something.

Our ears and brain are very good at integrating sound with the environment. A speaker that radiates evenly throughout the entire spectrum is like a conventional light bulb - it lights up the room evenly. A speaker that varies in radiation with frequency will give telltale signs to our ears - just like a spotlight produces a beam that is in one direction. When you couple sound with an environment like a room or space - again our ears instantly pick up on directional variations in sound and a spotlight or narrow beam over some frequencies is instantly recognizable even from the differences in reverberation from sound coming out a room window!!!

It is very similar to cupping hands over your mouth when speaking or using a megaphone to increase the directionality of the voice - we can hear this change in reverberant sound instantly.

So our ears brain are able to work out very quickly and easily that a beam of sound is NOT natural sounding. Only wide even dispersion sounds natural as it will evenly reflect off of the space around the sound source and the listener.

We are so good at this that standing in an acoustically treated totally dead room can make people feel sick - as the eyes and ears do not correlate what is seen with what is heard.

This is why horn speakers with uneven dispersion and a higher degree of directionality never sound natural except in a very small sweetspot and a nearfield seating position (this minimizes the uneven reverberation that makes it obvious that the sound is artificial).

AR chose small ensembles or solo instruments for their tests.  A symphony orchestra would be a far more challenging.

I don't think it's always easy to tell the difference since there have been specific occasions where I've been fooled, but in general, live sound reacts with background noises in a different manner than amplified music.  It floats above it as opposed to cutting through it.  Sorry for the obscure language.

I would have to say that audio gear is so good at this point that I am 99% happy with recordings sitting on my comfortable chair in my living room which has decent (although not perfect) acoustics.
I have difficulty EVER recalling hearing great sound at a live concert, although the experience alone was well worth the trouble of going in the 1st place.  When s great performer comes out on stage, whether it's Frank Zappa or the LSO, i get goosebumps anyway.  But for truly balanced sound and no coughing or other distractions, i can now die a happy person. Only ballet or opera, (or Woodstock) requires a ticket and a good seat (imho).  If you can get a string quartet to come over to your house and play, that (of course) would be terrific also...

...."Live v. Not...."

Dynamics, yes...but as an 'omni fan'....Ambiance....MHO, obviously...

...as soon as you move....(Generally*....)....*poof*...

( * = ...unless you've been very careful and/or very lucky to have the 'disposable income' to 'attend to the details'....in whatever manner or fashion you felt compelled to....Again, IMHO....)

I totally agree with everything Trelja notes particularly tone/ timbre, it's always been and continues to be so obvious to me. I find it remarkable how good recorded can get considering all the challenges posed. To me what is most important is conveying the emotion in the performance.