As a side note no two pieces of metal are identical either. ALL manufactured products have variation. If these variations fall within not tolerance limits they are deemed usable. If not they are scrap. Outward appearance is not the test for acceptance unless their are cosmetic tolerances as well like paint color.A couple of things. No two processors are identical, even if they have the same part number. I know that this is hard to understand if you've not worked in the semiconductor industry, but these things are not discrete pieces of metal that can be repeatedly cut to the same precise measurements. They are made up of things like silicon where no two on the same wafer even, are exactly the same. Through testing, they are determine to have certain characteristics to qualify them for a "part number". With memory chips, we built in redundant circuits so that if it failed certain tests we could blow some internal fuses and open up the redundant circuits. Our chips didn't get a part number until they were tested to figure out what they were. This is why the comparison of the two manufacturers is kind of futile... because the differences fall within the noise range of the product variance that would exist even if there were one supplier.
I think you also have this backwards by your statement. Apple spec'd the outside requirements, not specifically how the suppliers had to get to them.
Bottom line is that there is variance in all electronic components, period. There will always be attempts by techies to find the "best" of the "best" via continually running benchmarks.... one supplier, two suppliers, 10 suppliers... the combination of components and different possible test cases is so complex that its a bit of a futile exercise unless you just enjoying doing it as a hobby. The percentage of iPhone buyers that care about these minuscule differences is a tiny fraction.
I'm all for geeks having fun comparing chips. Where I get very frustrated is when they start taking gross advantage of a really good return policy by Apple, If they keep doing this then Apple will eventually be pushed to crack down and will probably tighten the policy... thus ruining it for the normal buyers that don't return a phone a dozen times chasing a unicorn.
And I also share your concern that abusing the return policy may induce Apple to tighten that policy causing people with REAL issues to get screwed.