They don't seat 80K anymore in a crumbling stadium. A major renovation in 1998 reduced the capacity to just a shade under 74K (still large by NFL standards) and upgraded the facility. At the same time, the Bills have launched an aggressive campaign to draw fans from Erie PA, and Rochester, Syracuse, and even Albany NY. They moved their training camp from SUNY Fredonia to St. John Fisher College in Rochester, to increase their visibility in a neighboring (and relatively prosperous) metro area of similar size.
(moving the comment back on-topic...)
Buffalo is one of the teams that really benefitted from the tightening of the NFL TV blackout rules. Before, fans in the eastern suburbs of Rochester could watch home games on the Syracuse stations. Eastside bars would use the game as a draw for customers. Now, if fans want to see home games that are blacked out, they have to attend in person. And many do - I heard once that Rochester-area fans make up about 25% of the ticket sales.
RE: PTBoardOp94's comment about stations buying tickets - IIRC, the TV stations would buy tickets if the game was close to a sellout (a few hundred tickets, but not 6K-7K) and donate them to charity, usually one involving children. The payoff? They get to broadcast the home game and get publicity (and a tax writeoff) for charitable works. And of course the human interest news story of the cute kids that got free tickets to the game.