This is the difference between the Football League and the FA Cup. Both competitions are played, but with very different flavours.
In league games Manchester United can play awfully badly, and still make up lost ground later in the season. With sudden-death eviction a possibility in the FA Cup, any village footie team has a chance, and the likes of Manchester United need to watch themselves at every game -- just like SCD exits of Gabby and Penny when "nobody is safe".
This makes for more shocks, more exciting games, probably a higher standard of play per game. In slow and steady league play only the top clubs with limitless cash for buying star players have any chance of winning.