I agree with you on this. Rafa has always had the pressure of the front-runner at RG, basically since the first time he won it. Also, we see the pressure weighing on them as their careers wind down, and each opportunity is fraught with the frisson of "last chance." This is, IMO, what tripped up Roger at Wimbledon last summer, and basically why the USO went 5 sets. Rafa felt the pressure to win there, and it was palpable.
As to Serena, I think it's worth mentioning that she also couldn't get the CYGS done in '15, I think? She was 2 matches away. She's a tough competitor, but the nerves can get them all, when the heavy rubber hits the road.