Let me first say that I like Steve Grogan and that I do not think that Tony Eason was a great quarterback. However, Eason has been demonized to an extent that is not warranted by his performance. In the three playoff games leading up to the 86 Superbowl, Eason had quarterback ratings of 132 (vs the NYJs), 102 (vs the Raiders), and 131 (vs Miami). In those games he threw a total of 5 TDs and NO interceptions. After taking over for Eason, against the Bears, Grogan threw for 1 TD, and 2 interceptions. His QB rating was 57 for the game. The Patriots were not going to win no matter who started, but Eason's perfomance in the three preceeding playoff games was strong enough for the coaching staff to pick him to start the Superbowl.
By the way, in the next season, when Eason led the Patriots to a division title and an 11-5 record, they lost their first playoff game to the Broncos, but Eason's QB rating in that game was 109, with 2 TDs and again NO interceptions. His career playoff QB rating (including the disaster of the Superbowl was 115.6 - better than Brady's 88.5 playoff QB rating! Grogan's QB rating in 4 playoff games was 49.1.
Before anyone says that this just proves statistics are meaningless when evaluating QBs, I will agree that Tony Eason in no way compares with Tom Brady. But I don't think that difference in actual production between Eason and Grogan is significant. People like Grogan more because of his attitude.