My Mexican made 8320 has the same issue where I can press down the area between the i/- key ad the esc key. The area beneath the shift keys will also compress if I press it since there's a tiny gap beween the grey and the rubber.

However, the keyboard itself has no play at all, so I wouldn't even notice that the grey faceplate depresses if it hadn't been mentioned here. My phone feels very solid. Absolutely love it.