The change to businessman was part of the big DC reboot after
Crisis on Infinite Earths in 1985-6. For Superman the changes were spelled out in
The Man of Steel, which is basically the source for the L&C TV show. This was a series to introduce the new version of Superman, with Lex as a businessman etc. There was even a collected version with the TV Lois and Clark on the cover.
I can't post this as a link, the site won't let me, but if you paste it into a browser it will give you details of the comic.
en.wikipedia.org/wiki/The_Man_of_Steel_(comics)
http://en.wikipedia.org/wiki/Crisis_on_Infinite_Earths
