> From a benchmarking point of view, the smaller die size shows a leadership in technology scaling for Samsung.
Almost certainly true.
> On the other hand, for Apple to go through all the trouble of dual-sourcing a custom designed part and launching on day one with both parts, suggests major sourcing problems.
Well... maybe. Or alternatively this is Apple throwing their cash around for long term leverage. They certainly can pay to have the initial design done on two different processes. And having done so, it puts TSMC and Samsung (and GF, who shares Samsung's process and would be an obvious third source) into a terrible bind: Apple can squeeze them with the constant (and credible!) threat of flight to a competitor.
See previous coverage of NVIDIA's rocky relationship with TSMC for an example of something Apple is probably trying to avoid.
The end user shouldn't worry, or even think, in what foundry was the chip fabricated in because it doesn't really matter if you are not the engineering team.
Similarly, I'm not sure how you expect reliability not to be affected by process; of course it'll be. But how often have you heard of a chip failing after it passes initial validation (something presumably apple does have a hand in)? It's not going to matter.
Now... it's true that all the media reporting so far seems to treat TSMC's 14nm and Samsung/GlobalFoundries's 16nm processes as "essentially the same from a design perspective" (though both seem to lag Intel's 14nm in density). But until parts reach the market we won't actually know.
Analogy: if you build one thing out of steel and one thing out of aluminum, you can get the same weight or the same strength, but not both.
