I disagree. Some teams never got a chance to go for 3 in a row. Broncos had two in a row before losing John Elway, one of the greatest QB's ever -- so I'd say they never really got a chance. I think those Broncos teams get overlooked in the discussion of best team ever.
The Bears, which a lot of people agree was the best team ever, was broken up following their Super Bowl. Had they been kept together, they could've done it.
Like I said before, I don't think the Patriots could beat the Steelers teams, the Broncos, 49ers, or the Bears. They may not have been able to get up and win 20+ straight games, etc -- but when they showed up for a game, they embarassed anybody wearing an opposing teams jersey, not just winning on a last second FG or such. That doesn't make the Pats feat any worse, but I think there's a difference between beating the second best team by 3 and beating them by multiple touchdowns.