Don’t be a moron and try to flex your $1000+ tablet, problem solved.
The people who whine about this probably share a lot in common with the people who are why McDonald’s needs to put “caution: hot” on cups.
The minor thickness increase makes very little difference if the materials are the same...
In normal use, it's not an issue, but if you sit on it or put it naked in a backpack with many other things you better have Apple Care +
I wouldn’t say minor, increasing the thickness in the strong axis will increase its moment of inertia exponentially.
Consider that the formula for the moment of inertia of a rectangle is 1/12 bh^3.
Height is a cubic variable in this instance, so increasing the height has a large impact.
Now consider that resistance to bending is governed by the Young’s modulus of the material (E), and it’s moment of inertia. E hasn’t changed, but I has increased exponentially.
The real problem is the span. The 12.9 is long. Consider it as an ideal span (each hand being a support). Given the span and the strength of the average human, you’re able to easily deflect it.
More than likely (I’m too lazy to do the calcs myself) the engineers at Apple found that to make it meaningfully hard to bend and shut up a few clowns on youtube, it would become quite bulky/heavy and annoy the lions share of customers who aren’t morons.