Crosby made a 31 yarder on the last play of the game on the road to beat 2011. 31 yarder...that's about a 95% make in the NFL. Those two kicks are his only game winners.
In 2010, he bounced a 53 yarder off the upright against Washington with one second left, again on the road, to send the game into overtime...we lost. A 53 yarder is a 50/50 proposition even for good kicker, especially outdoors. There are probably other game losers, but I can't recall the specifics, and 2 pages of a Google searches is my limit on this topic.
I found it interesting to see that Crosby holds the NFL record for most points scored in a player's first 6 seasons. Just goes to show gross numbers can be misleading.
You are spot on, I dug a little deeper with some what if scenarios as well.
Games in which a FG or FG's by Crosby that contributed to the win:
2007 - Sept. 9th 16-13 over the Eagles - Crosby kicks 3 field goals
2007 - Oct. 14th 17-14 over the Redskins Crosby kicks 1 field goal
2009 - Nov. 22nd 30-24 win of over the 49ers - Crosby kicks 3 field goals
2010 - Oct. 31st 9-0 over the Jets - Crosby kicks 3 field goals
2011 - Dec. 4th 38-35 win over the Giants - Crosby kicks a field goal - actual game ending field goal
2012 - Dec 2nd 23-14 win over the Vikings - Crosby kicks 3 field goals
2013 - Oct. 13th 19-17 win over the Vikings - Crosby kicks 4 field goals
Okay so, with crosby's field goals in the above games the Pack does not win and only 1 of those games was an actual last play game winning field goal
Games in which a missed FG or FG's by Crosby resulted in a loss:
2008 - Dec. 22nd 17-20 OT loss to the Bears - Crosby missed 2 field goals in regulation
2009 - Dec. 29th 36-37 loss to the Steelers - Crosby missed 1 field goal - this was a game where the wonderful Packers defense allowed a 16 play 1:58 TD to end the game, but the missed field goal also would have won us the game
2010 - Oct. 10th OT 13-16 loss to the Redskins - Crosby missed 2 field goals including a 53 yarder with 7 seconds left to play that would have won the game
2012 - Oct. 7th loss to the colts - 27-30 - Crosby missed 2 field goals
Okay in all of the above had Crosby kicked 1 or both of the field goals he missed the Pack would have one the game and only 1 of these was an actual game ending miss that would have won us the game
As hardright mentioned, he has only ever actually had 2 actual last play, game ending attempts and is 1 for 2 on them.
Conclusion, the Packers are generally so good that there are not many actual game winning attempts for their kicker for which I am grateful because there is nothing more nerve wracking for me watching football that have to hope your field goal kicker makes a last second FG for the win.