Thanks for the link, I was not aware there was a patent from Apple.
I used the term waterproof, as it is the most common one to illustrate the topic, and here is its definition:
waterproof |ˈwôtərˌpro͞of, ˈwä-|
adjective
impervious to water: a waterproof hat.
not liable to be washed away by water: waterproof ink.
nounBrit.
a garment, esp. a coat, that keeps out water.
verb [ with obj. ]
make impervious to water.
impervious |imˈpərvēəs|
adjective
not allowing fluid to pass through: an impervious layer of basaltic clay.
[ predic. ] (impervious to) unable to be affected by: he worked, apparently impervious to the heat.
And about the unbreakable glass: any material resists different levels of stress, for chemically tempered glass like the one used in the iPhone resists a lot of bending and some abuse, however some situations can apply enough stress on the the glass to make it shatter, or the presence of flaws in the glass plus the applied stress.
For glass to break there is a need of two key factors = enough stress applied to the glass and a flaw in the glass.
Tempered glass requires a stress high enough to overcome the compression layer and release the tension inside the glass core or a combination with a flaw to accelerate the release of the energy inside the glass, therefore it will break.
If your iPhone screen is broken in big size fragments it "could be" an indication of poor tempering.
To increase the glass resistance they could play with things like increasing the thickness, the tempering level and adding more protection to the sides.
The weakest area of the glass is the peripheral surface where it was cut and ground, therefore changing the design a little bit to have better protection to the sides can help to increase its survival rate, however this is the typical controversy that the designers and Apple love to challenge to make it a beautiful device.
The glass manufacturers will always struggle with the glass thickness and the different manufacturing difficulties, raw material variation, production throughput and so on.
And if they are researching other types of materials to have a similar forms, functions and feel they could take it to the next level.
As the current design is flat, it is easier to manufacture consistently, if they wanted to make it with a curvature could make it also a little more resistant but will increase the manufacturing difficulty.