In terms of engines Mark Webber at top is most comfortable, but it isn't everything.
We have seen Ferrari engines letting their drivers down at very important moments (Suzuka 06 & Hungary 08) so it is inevitable that Alonso has to risk engine from failing.
Though Button had nothing to do with Vettel crashing into him, while Webber/Hamilton was Hamiltons fault (more than Webbers)
In that case using that logic Massa was more to blame than Hamilton at Monza. Both Hamilton and Webber were up the kerb and couldn't brake in time to stop from hitting someone taking a good line around a corner.
That's the facts I'm afraid.
Check the video again, your memory might be a bit rusty on the Monza case - Hamilton only had one wheel on the kerb (and not any more than it would usually be) and plenty of room to turn more directly left without going more on the kerb, while at Singapore Webbers wheel was already going partly behind the actual kerb rather than on it.
how does someone defending thier position undercut someone else?
No he didn't. Hamilton was merely on the racing line. You know, the same line Webber took on every single lap when he wasn't impeded by any car ahead of him - from the outside of the corner to the apex and out again.
You truly have an odd view of racing. Do you drive under the same assumption on the road (or track) that the car on the inside line regardless of actual track position is in the right, even if he his clearly behind? That's as ridiculous as saying Massa should have made room for Hamilton in Monza.
Of course he was. It's on video and on the picture I posted a page back. Hamilton was clear of Webber. Just because Hamilton stayed on the racing line and didn't shut the door which allowed Webber to close the gap again somewhat doesn't make it any different. Starting at least 300metres leading up to that corner, Hamilton was in position 3 and Webber in 4.
Even if we agree that both were fighting for position, the fact remains that Hamilton was ahead and on the racing line and Webber was attempting to re-take P3.