Tomic was standing 5 meters behind the baseline to return the second serve of Brands. Try that against Federer and see what happens.
Also - Brands' poor returning flattered the Tomic serve big time - he used the guess which way approach most of the time which meant he guessed wrong a lot.
Federer was Ok vs Davydenko but a little unspectacular. He did what he needed to against an opponent who can make almost anyone self-destruct. In some ways Davydenko's ability to change the direction of the ball will have been good practice for Federer since Tomic does it too - just with less power than Davydenko most of the time.