I'm sure it was a cost cutting measure but even so the belief that a one piece back is superior in tone is like one of those urban legends.
I defy anyone to play 5 great sounding les pauls and accurately guess which one is a 1, 2, or even 3 peice back. There's so much more involved in a guitars tone than the number of peices in the back. Look at some of the best sounding old strats on record. I guarantee the huge majority, if not all, were 2 peice bodies at least.
True story: about 12 years ago a guy I know had his original 59 les paul, and I mean original, smashed by a very angry drunk in the parking lot of the venue he played at. Had to do with a girl, etc...
If you could have seen that guitar you would have cried. It was smashed literally to pieces. The guy held it by the neck and brought it down like a hammer separating the neck from the body and then proceeded to hammer the body off a brick wall till there was around 5 pieces of it around the area.
If there is anything lucky about it, it's that the neck was immediately discarded and not smashed with the rest of the body. other than a small chunk that broke away where the body meets it there was no real damage. The body was another story. The other guys in the band picked up the pieces and the guy just put it into a case for about a year. He eventually came across a friend of mine who is amazing with this type of repair. It took almost a year but the body was completely put back together and then reattached to the neck. Some of the wood had to be re matched with new smaller pieces so it would fit properly and the neck had to have a new tenon cut but when it was all put back the sound of that guitar will give you chills.
One of the best sounding guitars I've ever heard, period.
The repair was done so well that it's vitually impossible to tell unless you're right up, inches away. You can see some fine seams in places but from 3 feet away or more it looks untouched.
The guy who did the work has pictures before and after and if I hadn't seen them there's no way I'd believe it.
I figure there might be better sounding pauls out there but I've heard a lot of them and have never heard one better than this one and I just heard it again about a month ago.
I don't know which of Joe's guitars may be one or two piece bodies but I doubt very much if Joe worries about it. It sure hasn't hurt his tone one bit.
A very well known guitarist once said "if it sounds good, it is good".
I think as players that's all we should worry about.