According to the folks at Bell Labs this idea is early stereo consumer electronics industry marketing rhetoric that has no scientific basis at all. Our hearing responds just dandy to the phase relationships between low frequency sounds arriving from different directions.
As for mixes intended for stereo LPs, obviously it would be foolish to create ping-pong bass drums. In pop music we are generally talking about pan pot stereo rather than real stereo. Quiet as it's kept, when the record stores began refusing to order mono records, we just started panning most everything important to the center. Mono actually won the mono vs. stereo "war." This is why many of us pop music types rolled our eyes when quad came along.
I would also credit the folks at Ekektra, Warner Brothers
and A&M for moving the record business from just selling singles to high school and college kids to selling them albums. Today's music industry has forgotten what it took to make a compelling record album that kids would buy instead of a single.
-- Bob Olhsson Audio Mastery, Nashville TN Mastering, Audio for Picture, Mix Evaluation and Quality Control Over 40 years making people sound better than they ever imagined! 615.385.8051 http://www.hyperback.com