Yeah but there were years when, throughout the season, the Bills were the best team in the NFL and could beat anyone. It only seemed to be when it came to deep in the playoffs, another team would raise their game a bit and the Bills couldn't seem to match it. Either that or the Bills would slump slightly right at the end of their campaign.
They beat the Giants during the '90 season and the Cowboys during the '93 season and went on to lose to both in Superbowls. In the four regular seasons where they lost Superbowls they were 14-2 against the NFC. One loss was against the Lions ('90) and one was against the Redskins ('91). Both losses were in the last game of the season, when the Bills had already wrapped up their division and home field advantage.
They were also 4-1 (with the one loss being the '91 Redskins season finale I mentioned above) against the teams which beat them in the Superbowls during those four regular seasons.
It seemed to be only when the Superbowl came round that they would screw up against the NFC. They just couldn't seem to 'peak' when it mattered most. It still kind of baffles me. They were a great team but couldn't make it over the final hurdle.