I don't know how you could possibly think that "half" of your 4 to 6 GB of data usage could be from "system services" and "advertizing network services integrated with applications." There is NO way this is the case.
I have 4 smartphones on my account, 2 4G androids and 2 3G iPhones. With your reasoning, I should have ~2 GB of data usage JUST for the items you blame half of your data usage. With my 4 smartphones, I have less than 2 GB TOTAL DATA USAGE which would include those items. I don't see why my "system services" and "advertizing network services intrgrated with applications" would be any less of a data hog than yours.
I would check for other culprits concerning your data usage. It is doubtful those are using as much data as you believe.