FYI, while a SAPPHIRE crystal is more scratch resistant, it is also much more brittle than HARDLEX (Seiko's proprietary mineral glass). Seiko could use any glass they want but they use HARDLEX in their sport watches because of this fact, they sacrifice some scratch resistance for better impact resistance.
Recoil_RobI appreciate the note, but I think that Seiko uses Hardlex over sapphire not for better impact resistance, but for better margins and profits--and to keep the retail lower. The Seiko Sportura line uses sapphire, but at a higher price. I agree with Butchram that sapphire is significantly better crystal material unless you use your watch face as a hammer. Imho.