The general consensus -even within the teams management- is that he let it happen deliberately.
Perhaps not as obvious as some previous incidents of German drivers coming together with rivals (Schumacher) but if you compare Rosbergs move and positioning on the track relative to Hamilton with Vettel making a similar attempt on the previous lap before thinking better of it and bailing out, -despite being in a stronger position- makes it that bit clearer, to me anyways...

