can your phone bend to 90 degree? Wow.. that good model u got.. and as for the availability of corning, in fact, a lot of china manufacturer used the terms gorilla glass to promote their sp, its just most of them are fake claims.

this is imos Solid EX Corning glass sp after 4 months of heavy use on my iPhone 5. Let me know if any of the sp in the market can have this oleophobic effect after 4 months of heavy use. And also, if you might forgotten, oleophobic coating helps to reduces the fingerprints and stains on your screen.

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the sp requirement is similar with the actual screen. n it gives u the reason y corning is needed.
Wanted to know why u like phone without sp? clarity?
your question on why need another corning on top? so that u will have the same feel as naked screen but with extra protection better than a soda lime glass which only gives u protection but bad user experience. hope this explanation make sense.

or u can think it this way, why do people go for Camry when a proton saga can also drives them from point A to point B? Then u should have the answer why corning sp and not soda lime sp.