1. In general, glass is brittle and easily break upon impact. especially a very thin piece (the case of a screen protector). if the purpose of the glass screen protector is to prevent scratch, yes it does the job. But to cushion impact, I wonder ... That is why glass screen protector cracks easily, which may lead to us believing that it saved the camera.
2. Camera manufacturer use plastic over glass as the LCD window for a reason. In addition, there is a clearance between LCD window and LCD. so should there be any impact, chances of it hitting the actual LCD is kinda low.
3. So if the purpose of putting the screen protector is to prevent scratch, the plastic ones might do the job. However, plastic are very prone to scratch, thus glass may be a better choice.
To conclude my lengthy post, if the screen protector serves only to prevent scratches on LCD window, there is no need to buy 1 that cost much more than a LCD window replacement.
Cheers and Merry Christmas everyone.