Earlier quoted context omitted.
"as far as i'm concerned, anyone who dismisses sapphire crystal on a watch as some kind of useless feature isn't to be taken seriously about watches, smart or otherwise." Compared to gorilla glass, on a watch that lasts 3-5 years? Why? What do you think sapphire buys you? Have you ever done tests (I know for a fact that at least one of the very high end watchmakers didn't)? In any case, high end watches last 30 years…
sapphire's selling point is scratch and crack resistance, i.e. strength. the ability to last 30 years is a byproduct of that strength. you can put unused pyrex on a shelf and it'll last 30 years. but try dropping it on your kitchen floor. every single non-sapphire watch i own has scratches on the glass. i've broken the screen on every single generation of phone to date. however, none of my sapphire automatics have a…
So is "crack resistance". Do you mean when someone tries to indent it? DO you mean when flexed in some other specific way? Do you specifically mean when dropped?
Materials have very different properties depending on what you are asking.
You can't just combine these very different things into some measure without some actual methodology for doing so.
"you just sound like a person who hasn't worn a watch for very long, or don't have a range of watches to compare against each other. "
I have done both.
"and i disagree with your fundamental point, which is that sapphire has no value on a device that lasts only a few years. of course it does - it's extremely strong material that withstands impact. "
This is just fundamentally false. Sapphire does not withstand impact compared to gorilla glass (or almost any glass). Sapphire is also very well known to be brittle.
But you don't have to take my word for it, it's been tested:
http://www.ubreakifix.com/blog/sapphire-screen-drop-test-the...
Sapphire cracks at 3ft drop, gorilla glass doesn't.
Additionally, my little materials science book on moh's hardness actually says:
"Brittleness basically indicates how resistant the material is to plastic deformation. A very brittle material will, when placed under stress, break/fracture rather than bend. In the case of a sapphire crystal versus a glass crystal, the sapphire is considerably more brittle. As a result, a sapphire crystal is more likely to chip or crack than is glass counterpart if both are subjected to an equally hostile stress (banging, etc.)."
You can find plenty of research on both if you want unbiased sources. I'm a bit lazy to go look it all up for you, but start here for sapphire:
http://arxiv.org/pdf/0908.2058.pdf
Short version: Sapphire is brittle. It fractures and chips when dropped or deformed in that manner. Most ion strengthened glasses are less brittle. Relative to sapphire, they tend not to fracture or chip when dropped or deformed in that manner
There are of course, materials that are even better for drops, but worse for abrasion resistance, like polycarbonate.
Additionally, once cracked or seriously scratched, the game changes for both, of course, as it's a matter of crack propagation, etc.