They justify it by saying that fans don't want preseason games. They never suggest just doing away with two preseason games and replacing them with scrimmages that fans can attend for FREE. They're tied to a 20-game slate for profit and now figure they can squeeze more money out of concessions and parking by switching to 18 regular-season games.
That's what I also don't understand. Why is the 20 game slate required? Like you said, money. They're not worried about the quality of pre-season games, if they were, they would just cut it to 16/2 seasons, they want to have as many games as possible where fans fill the seats. They know the 4th PS game is a joke, which loses them revenue.
I'm really torn on the 18 game season. As a fan I'd like to see more games, who wouldn't? There are a lot of drawbacks to it though..
A) Pats old records become obsolete
B) More games = more margin for error. This lowers the importance of each week by a fraction. Not a whole lot, I mean it's only 2 games, but we all know the more games, the less each individual one means (see baseball)
C) Players really should get a raise. I know it doesn't really effect me, the viewer, but in the side of entertaining millionaires vs boring billionaires, I'm on the millionaires side.
If there is a lockout, It's going to be really horrible to see someone like Brady miss two full seasons in his prime, that's for sure.