The protection circuit looks completely arbitary. Why a zener at SDA, why not at SCL or VCC?
Capacitors at SDA and SCL have to be small (maximal 10 pF range) and don't actually provide releavant protection, e.g. against ESD. At best they cut RF interferences, e.g. if the board ist placed near a GSM antenna. I2C data rate and SDA pull-up values have to be known. Vcc filters can use 100 nF up to uF range without problems.
Generally speaking, the chip may either need no protection at all or more effective protection, depending on the application enviroment. The fact that you see this circuit in a product doesn't necessarily imply that it's well considered or even serves a purpose.