Hamilton was lucky that he didn't have the braking issue earlier on!
It sounds like the brakes didn't fail, he explained that they went into a default mode for some unknown reason but after changing settings they came back. Effectively the amount the pedal travels is controlled electronically. They have pedals set pretty hard as you don't want to completely extend your leg with full pressure all race. He said all of a sudden the pedal just went right to the floor which it does as default mode, changing settings it worked again.
That it happened on both car at the same point somewhat suggests a bug in the code somewhere that caused it rather than a problem with the brakes themselves. Still, not ideal and happened at the wrong corner at the wrong time for Rosberg so I genuinely feel bad for him about that. Though much as with his "had I gotten pole I'd have definitely won the race" attitude last race, he had the same "without that problem I'd definitely have come second"... a tad irksome. Kimi still had tires left and that car has good straight line speed. I thought with another drs straight left to go and having cleared that last traffic and been really close he might well have gotten him into the first corner on the last lap, possibly elsewhere but that was the most obvious chance.
20-30bhp isn't all it's about though. Downforce, the merc can go faster if it dropped some downforce, though obviously you can bolt on a bit more down force if you have more engine power without the drag slowing you down. It should help but there is nothing to say Merc won't bring their own 20-30bhp update and effectively cancel out any advantage.
I think one of the most interesting changes we'll see through this season is the Vettel/Kimi battle. Vettel is all smiles and friendly now but if Kimi starts leading him in the title fight, if he starts taking points off him by actively passing him on track or beating him in qualifying. Things could look very different if/when Vettel is in a real fight against Kimi.
For Hamilton though, Vettel, Kimi and Rosberg sharing out second places is as much as he could hope for. He was what, trailing Rosberg by what 4 points after the 4th race last year, this year he has a 27 point lead on 2nd place.