My other thought is that (with hindsight) it might be better to have a team quota for engines. That gives them a chance to smooth out any problems due to bad luck with one driver, but maintains the same number of units used. The downside is that some teams would give the number 1 driver a new engine nearly every race, the number 2 driver would have to make his engines last longer, or use second hand engines passed down from the number 1.
Personally I think the driver already takes a large enough penalty with his DNF that any further penalty is stupid. I think that if the engine expires in a race
the team should be allowed to install a new one with no grid penalty for the next event. If there was no engine freeze this would be a bad idea, but since they are frozen I don't see the problem with this. I think with the current situation it would be a real shame to see the championship determined by engine penalties rather than the drivers performance.
As far as Vettel being an engine killer, I think its more down to lady luck. Even if he was driving overly hard both engines failed overly prematurely.