I think it likely that, for the vast majority of "casual football fans" the "greatest upset in football history" in Super Bowl III overshadows all the accomplishment of the Don Shula Colts.
And if that doesn't do it the loss in the 1964 NFL Championship game does.
For almost a decade "Shula's Colts" were (with a few exceptions) one of the best teams in the NFL, almost always in the top 4 in the league.
From 1964-71 (with Don MCCafferty running the show in 70 & 71) Baltimore had one of the best defenses in football to go along with the offensive talents of players like Ray Berry, Lenny Moore and, of course, Johnny Unitas. I'm pretty sure we could all name a dozen Hall of Fame or HoVG Colts players from that era.
But, just as in "real" history, the public remembers only the largest, most spectacular of events and so the 60's Colts are remembered not for their years of sustained excellence or incredible players but for their unprecedented and unexpected failures.
Another thing to take into account regarding SB V specifically is how poorly both teams played.
Winning a Title by being the survivor of the most poorly played Championship game in recent memory does not give one the historical recognition that winning by a landslide might.
Had the Colts come out and dominated the '70 Boys or even won in a hard fought, well played contest then the 1970 Championship might be seen as the validation the franchise and the players were looking for: the crowning achievement of a decade of excellence.
Instead they were the least pathetic team in a contest of ineptitude... and as such they are remembered.
http://www.pro-football-reference.com/t ... t/1970.htm