The 20+ minutes are pure advertising - you also have to note that most programming, including the Super Bowl, has all the other advertising built into the program (Pepsi half-time show, Chevy Post-Game show, Home Depot tools to the game, Bud Light hit of the game, logos on jerseys, branded apparel being worn by the announcers, etc. etc.)
It's only time until the NFL starts seeking more cash, and sells adds on the field and sidelines like the CFL, and eventually will have branded jerseys that many soccer clubs have, and even targeted local ads like MLB and the NHL have overlayed onto the broadcast.
Global even tried to do the overlay on the field with Harvey's ads and other advertisers during the Super Bowl about 10 years ago - that was one year simsub was horrible for Canadians.
It will probably come to the point where we count the seconds per hour that advertising doesn't exist.
The NFL is probably the best for not having continuous advertising during the game - other then jerseys and shoes that aren't blatant.
I always laugh when sports, like Formula 1 that I am a fan of, advertise that they have advert free races on some foreign networks - when the race name, cars, and everyone involved is walking billboards...