Series opening/closing credits being changed for "reasons" is annoyingly common.
In the 80's Star Trek's first season was standardized so all but one episode has the same Fred Steiner arrangement, replacing the Alexander Courage electric violin theme (now there's debate as to how many episodes...
"Bone-anza..."
It is a handsome box set. I got Gunsmoke for $30 less than what Bonanza is going for now, so I'll probably wait for the price to drop or Christmas money.