Also, Eastern Air Lines had marketed their new B-727 and DC-9 aircraft as "Whisperjets" in TV and print ads, even going so far as to put "Whisperjet" titles on the aircraft themselves. (They'd later title the widebody L-1011 and A-300 aircraft as "Whisperliners" as well)
This gave Eastern a distinct marketing advantage, as customers would often ask other airlines, "So, do you have Whisperjets too?" The lack of using such a title was a perception problem for the other majors, and they needed to have another small gimmick of sorts to help sell themselves and show that EA didn't exactly have the leg up that everyone thought they did.
So American's planes (which had previously been known as "Astrojets," cashing in on NASA hype in the agency's heyday in the 60s) became known as "Luxury Jets" and "Luxury Liners," depending on if the plane was a narrowbody or widebody aircraft.
"In this present crisis, government is not the solution to our problem - government IS the problem." - Ronald Reagan
Comments made here are my own and are not intended to represent the official position of Alaska Air Group