If Kieswetter makes his visibility better by making the gap bigger between the peak of his helmet and grill, then he has himself to blame really!
Same thing with Broad if he does the same, AND also uses a model of Ayrtek/Adidas with less protection level!
The way I look at it, I have made the grill space a little bigger on my helmets to increase visibility. It's a minimal risk but I know that if a ball gets though, then I only have myself to blame for altering the grill settings. I would hate for a helmet manufacturer to fix the grill in place so that I can't alter it!