I was looking for that Chuck Rainey quote too, knew I'd heard it somewhere. But its interesting phenomena.
Couple years back I got a dep with a very good Beatles/60's outfit. They were all retired with wifey on keys, hubby on guitar and a very good singer/guitarist..plus drums, all singing harmonies. Dont think I've ever worked so hard... There were no charts or anything. 60 tricky tunes in 2 weeks and I did drop a few clangers here and there.
They were tight as a wotsit and I dont think the singer was totally impressed. Most of the time you can get away with it... but playing with them was def pushing the envelope so to speak, needless to say I didnt hear from them again.