Federer played excellent tennis, even in those tiebreakers, he didn't exactly choke or played horrible, he just didn't play his best. There is a difference. Federer fans expect Federer to play perfectly in crucial moments, anything less, it's horrible.
I have a simpler explanation for why Djokovic is better in crucial moments, it is not mental scars for Fed or mental weakness, it's their types of games. Djokovic is the cleaner ball striker who makes less UFEs and takes less risks, Federer is the streakier ball striker and one who takes the most risks. In tiebreakers, you expect Federer to be more shaky, hit some great winners (he hit a couple of exceptional winners in breakers) but also miss more. Federer's riskier, less tight game will be prone for more errors but sometimes pays off... The key for Federer is the serve, he can't rely on his ground game to be tighter than Djokovic's in these critical moments, especially with the tension and nerves at play. 9/10 times Federer will be more shaky in these moments and under that type of tension or pressure, it makes sense that it's more difficult for Federer to play clean tennis than Djokovic. The, again, is the serve, Federer has to serve really well in the breakers, this is where i think he missed the mark...