As you say, it's all in the perception.
When Wilfork forced the fumble right before the half, I turned to my wife and claimed "that's a season changing moment right there." One could argue that the Bills were about to go ahead 21-7 AND get the ball first in the 3rd, to where they likely would've gone up 28-7...
By keeping the game within 1 score at the time, they allowed the team to go into the half only down 14-7, which was great considering how bad it could've been. Yes, they went up 21-7 to start the half, but it likely would have been worse. I'm definitely going with the game changing moment, and potentially even a season changer, considering that they would've been starting with a 1-3 record had they likely gone down 28-7 when the Bills scored first to start the 3rd quarter.
As far as the SEA game, yes...we had a chance to have a great half. Brady had almost a 75% accuracy rate in the first half w/ 2 TD's and 0 INT's. By kicking the FG instead of the intentional grounding, they would have scored 20 already on the "mighty" Seahawks; thus proving to double score on them on the road, and it would have likely helped to take the crowd out of the game too.
Most importantly, it would have obviously been the deciding pts in a one pt loss, considering that they would have won by 2 points instead.
In other words, instead of it having been 23-10 NE, it would have been 26-10 NE. It would have been extremely unlikely that SEA would have scored 2 late TD's including both 2 pt conversions, and even so---it would have only sent the game into overtime.
Both were certainly game changing moments, but allowing the 46 yd TD down the middle with 30 seconds left was certainly another game changing moment, considering the current circumstances...