Well, clearly the reinstatement of the old OTEBD regs helped McLaren as did Hamilton being 'perfect' in Q3 and the Grand Prix.
Add to that Alonso not being as 'perfect' and you get a McLaren victory.
Alonso made an error where he let Vettel by.(which cost him some time)..and then Hamilton just mugged Alonso for the leadership of the race. Alonso certainly lost the win when Hamilton over-took him around the outside of Turn 2.
If the OTEBD levels were at Silverstone levels, i'm afraid Hamilton wouldn't have won this race.
1] Alonso repassed Vettel fair and square on track after the error so that was irrelevent.
2] The drive of the McLaren out of 1 and into 2 was so much greater, Hamilton effectively passed Alonso as soon as he hit the accelarator comming out of 1, Alonso was off throttle and battling to turn the Ferrari into 2 and 3 sweeping Left, some say better defence in that instance would have worked that said he was never in a position to defend that. Some suggested a Hamilton on Webber though the difference was Hamilton being inside well into 2 and both cars were on run in tyres/ up to temp tyres.
I think Ferrari kept the gap close on the basis of stability on straights and being good on the brakes, but into corners requiring throttle input into a turn the Ferrari was anything but good. Maybe the nature of Silverstone was also a one off for Ferrari, Straight, Brake, Straight, easy turn...etc.