I am seeing this as well on three iPhone 4 units and an iPhone 4S.
There is a second Diagnostic and Usage On/Off under Location Services - System Services.
the odd thing is that two of the four phones only have a couple of non-stock apps loaded - and two of the phones are very lightly used as primarily phones - and yet one of the three is using close to or more than 200MB a month - and it is NOT used for GPS navigation or browsing the web or checking email except when at home connected to WiFi.