Jenson might deliberately drive slower than he is capable of at times in order to conserve tyres but I don't think he's ever given up laptime to make sure his gearbox doesn't give out.
It would be obtuse not to conceded that the driver has some impact on the reliability but, and I can't remember if anyone has ever come up with a plausbile explanation for this, lewis's stellar relaibility record in his first 3 years makes it difficult to point to him as a 'car breaker'.
In the races where he's been leading towards the end or when he has conceded that he was unlikely to gain positions, he's often turned down the revs and cruised to the finish line.
Has as been pointed out earlier Hamilton was driving far harder in 2007, 2008 and 2009 and wasn't having reliability problems, this is just all supposition to meet an agenda
The regulations weren't as severe regarding gearbox and engine life in 07 and 08, so that may also have been a factor as you could simply change damaged or overstressed components earlier/more often. That still leaves '09 of course.
In any case, as several others have stated, it is hard to know to which extent the driver influences component life. But I think it is fairly obvious that the driver contribution is strictly more than 0 percent -- but whether it is 0.01, 0.1, 1 or even 10% ? I simply don't know.
Do I think Lewis has contributed more to his car failures than Jenson in their 3 years together? I'd be inclined to say more likely than not. But that is indeed only speculation based on the perception that Jenson generally strikes me as smoother and more careful/cautious/tidy in his approach to racing.