Confirmation bias is the tendency to search for or interpret information in a way that confirms one's own beliefs or hypotheses. Romo's ratio is 8/4 in the six playoff games, and 4/8 in the three regular season elimination games. The only way to conclude that Romo's performance drops off in the postseason is to redefine "postseason."
That means lumping in playoff teams with non-playoff teams, with the only common denominator being that a loss ended their season. Is this justified? Compare the teams Romo had for these games minus Romo and the pass offense. Combining the Cowboys' season rankings in pass defense and rushing TD, these are the teams Romo has had to work with:
2006 12th (20th, 3rd)
2007 8th (5th, 10th)
2008 21st (20th, 22nd)
2009 16th (16th, 15th)
2011 28th (25th, 30th)
2012 28th (29th, 27th)
2014 9th (13th, 5th)
Playoff seasons are in bold. Romo had 4 TD/8 turnovers in these games in years when the rest of the team ranked 21st or worse (non-playoff teams). He had 8 TD/4 turnovers when the rest of the team ranked 16th or better (playoff teams). We can't just assume that this is a coincidence. On the surface, it looks like Romo has played better when he's had good teams, and has tried to force the issue when he's had bad teams.
The average point margin in the three regular season "elimination" games when he committed his turnovers was -13.75 points. Up until 2012 in Washington, it was actually -21.4 points. Until that game, he'd had zero turnovers when the opponent had less than a 13-point lead in the game. So while it's safe to say that Romo was pressing in that game in Washington in 2012, there's no evidence of a pattern in either of the other games.
In order to conclude that Romo plays poorly in "elimination" games, you'd have to show that his performance depends on the mere fact that it was an elimination game -- and that it doesn't depend on factors like the score of the game, or the quality of the team around him.