I guess its cool having a metallica tattoo on your wrist. That is all the big 4 is. It's a huge Metallica show. They play 2 hours, have the huge stage show, have the fonts all in Metallica fonts. Metallica didn't do this for any other reason than they knew it would draw 100k fans at each show. The big 4 is nothing more than a Metallica headlining show. Anthrax has 10 percent of the audience in the stadum when they play their 30 minute set. It sounds a lot cooler than it really is.
It's like being in a local band and you get the first opening slot playing for a semi large club act and then going and telling all of your friends that you just played a show with a 'insert band name here' band.
In reality you just played in front of 10 people as the fans of 'insert band name here' were in the parking lot drinking beers. Anthrax is the same thing. They are playing while the Metallica audience is outside drinking beers and getting home from work