Your question is invalid because you presuppose that a design flaw entails that Apple "didn't figure something out". That is not what a design flaw logically entails.
It is a design flaw because it serves no purpose to have two different materials on the back, since one material is perfectly sufficient. Using two mars the aesthetic quality Apple is known for. For these two reasons, it is a design flaw (if indeed the rumors are true).
I still think that the two material back designs are just prototypes, since I don't think Apple would actually produce something so shoddy looking.
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How exactly will landscape mode benefit from a taller display? It will be just as useless as it is now.
If Apple knows what it is doing, it won't make an elongated iPhone since it adds very little value compared to keeping the same display ratio and increasing the size to 4.0 (or whatever they go with).
flaw [countable]
1 a mistake, mark, or weakness that makes something imperfect [= defect]
flaw in
a flaw in the software
serious/major/basic/minor etc flaw
a slight flaw in the glass
A design flaw (=a mistake or weakness in the way something was made) caused the engine to explode.
2 a mistake or problem in an argument, plan, set of ideas etc
flaw of
Beautiful scenery does not make up for the flaws of this film.
flaw in
There is a fundamental flaw in Walton's argument.
fatal flaw (=a weakness that makes something certain to fail)
3 a fault in someone's character:
Jealousy is Othello's major flaw.
the President's character flaws
Just to make sure we are speaking the same language.