I followed all of these things too and still had scratches. Not severe, mind you, but they were definitely there. My theory on why? I live two blocks from the beach and sand is everywhere, whether you realize it or not. That's why I use a screen protector. At the end of the day it's still glass and no amount of babying it will always be foolproof.
I don't live at the beach, but within 20 miles. No scratches noticed on the glass.