I think there are certain games you can simply eliminate from this discussion. For example, was there ever really a chance that the Pats would blow out the Rams in 01? No, if they had any chance to win that game, it was going to be close. While I wouldn't go that far with any other matchup, it's not weird to me that the Eagles in 04 and Seahawks in 14 were close games. One was a pro-bowl laden #1 seed (I think?) and the other was one of the best defenses of the 21st century who had already won the bowl (in deliciously dominant fashion) the year before.
I also think the 2011 game against the Giants was more even than we would like to admit, and Gronk being hobbled really changed the complexion of our offense. A blowout there was unlikely as well.
While it should never be surprising that a SB is close, I do think we had better teams than the NFC opponent the other four years, so you could say the loss/close win was unexpected. But I've always felt the Super Bowl is a really different kind of game, and it's hard to predict how players and teams will respond to it. So I'm not sure that a sample size of four "unexpected" results is enough to find a correlation.
This is a collection of specifics, which is fitting to gather data a case at a time. Each particular scenario for "closeness" is unlikely to be repeated exactly the same way, yet another closeness scenario takes its place the next time.
There are larger secular trends that need splainin:
Those of us who remember the 80s and early 90s remember the era when everybody said "I don't care who wins, I just hope it's not a blowout." That's because every dang year it was a blowout until then.
I think a good "cutoff" for this tendency was the mid 90s (going from memory.) I know the Pats were actually IN the 97 Super Bowl almost until the end. Then there was that last-second reach for the goal-line in the Tennessee-St Louis Super Bowl. And the Terrell Davis Super Bowls to end Elway's career. All of that sudden close-gameness started in the mid 90s, AFTER the tyranny of disparity that was the Buffalo Bills one-conference dynasty. Then in 95, SF beat SD 49-26. I guess SD should have changed their name to the 26ers, right?
What exactly happened from 1996 onward?
Hmmm. For one thing, it was a throwback dynasty game, Dallas-Pixburgh. (PS, Dallas won, 27-17). Maybe they had that in their heads a little, they were equals.
Less sentimentally, the salary cap was introduced for the 1994 season. It's easy to imagine that there was a little time for the new rules to take hold.
Very soon thereafter, the Patriots began their new kind of dominance - season after season, vs. non-stop blowout wins for a short period (although they also achieved this feat, for 18 games in 2007. Just not for 19.)
Belichick often emphasizes how narrow the margin of victory is in the modern NFL, and he preaches situational football. You guys ever see that NFL network commercial that shows some team breaking the huddle with "'Dominate' on 3, 1, 2, 3 DOMINATE!"? Well, that's great if you want to get psyched up for one game. But compared with earlier years, it's sort of like saying "Good luck on 3!"
Now, that said, our results have been skewed for half the SBs since 2002, that is, the SBs that NE has played in.
So take away those appearances, and for all we know, we'd still have long stretches of blowouts in SBs.
Take a team that always has a crappy draft position, then take away half their draft picks... it's not rocket science that they'll be living by their wits to an extent, not thriving because of an unexpected edge in talent at every position.
Era vs era, I
think something like the Patriots were always going to be the answer to "how do you consistently win in the salary cap/free agency era." But this model was not destined to be built by the Patriots. Another team might have gotten there instead. Several might have figured it out. Having that 1, high-impact, initially low-cost, always reasonable-cost piece (Brady) is a HUGE advantage. Having him all-in is more huge.
Fortunately, the Pats jumped on Brady with alacrity in the 6th round, before anybody else had an opportunity