Right. No matter how weak a division they may have played in, if playing a weak division was a practical guarantee of going unbeaten, surely we'd have seen it more often than one time.
Funny enough, quite a few good SB championship teams had some head-scratching "WTF?" losses on their schedule, not counting end-of-season "we've locked up HFA, so let the 3rd stringers get some playing time" losses.
'04 Patriots lost to a Dolphins team coming in at 2-11 (had they not lost that game, they would be a good candidate for top 5, no doubt)
'03 Patriots lost to a Steve Spurrier led Redskins team finishing 5-11
'98 Broncos lost to an 8-8 Giants team
'94 49ers - Eagles (7-9)
'92 Cowboys - Rams (6-10)
The '84 49ers one loss was to a 9-7 Steelers team, although they did make the AFC Title game