Several sports outlets have noted the last team to take games 6 and 7 on the road is the 1979 Pirates. One knows that is a long time ago - #1 because the Pirates were involved and #2 The calendar tells us that it has been 33 years.
There is a bit of an illusion in that 33 years. The Cardinals aren’t really up against a phenomenon that only occurs once every three decades – Not all World Series find the Away team down 3-2 after 5.
As you can see the team that came the closest to the double road gm comeback was the 1997 Indians. In fact they came within a Save opportunity by Jose Mesa of being World Champs. The other 5 contenders all bowed out in game 6 - with 2 of those 5 being Phillies teams, including the Joe Carter game.
To me it is worth noting if you have 2 evenly matched teams the odds of either one winning back/back games is 1 in 4. The down 3-2 on the road scenario has only happend 6 times. This leads me down the small sample route - it hasn't happened in 33 years simply because it the opportunity doesn't occur that often (except to the Phillies). A probability person may conjecture that the Cardinals Winning the 2013 World Series is expected, it is just evening out the odds (or returning to the mean)
2013 PostSeason Cardinals
2013 PostSeason Red Sox
Jose Iglesias (Now with Tigers)