To be honest, a lot of these guys have become more mentally committed in their matches against Fed (except Rafa who always knew his game troubles Rog). In previous matches, they would basically go away when Fed gets on a roll - this doesn't happen anymore. This was clear to me in the Dubai semi- Berdy won because he refused to blink.
I do believe that Fed has to realise this - there so only so much 'tweaking' he can do to his game. It's quite possible that the killer instinct is not there anymore, just a natural part of the aging process.