I have a general question about surround sound.

What is the big deal about multichannel music? I see where many of the new SACD's are multichannel. Does this make the recording seem more lifelike? When we go to a concert, the music only comes from in front of us. Isn't that the purpose of the two speakers in our stereo systems? Why do we need two behind us? I understand about ambient noise, reflections, etc. It just seems to me that music is more accurately reproduced with two channels rather than multichannel. Could I please get some feedback and whether you agree or disagree with me and why.