That's pretty common, and is one of the reasons for some of the third party exchange clients on Android devices. At least one of the early ones (Nitro?) maintained its own separate data store for email and possibly other things so that when policies were used to wipe data it could wipe only the data in that app instead of the entire device.
The counter to that is that now I believe there are a bunch of Exchange clients on Android that will simply ignore server policy or where handling of policy can be controlled in the settings, which kind of defeats the point.
The original point of all those policies was to be able to erase supposedly secure content if the device was lost or if someone left the company for whatever reason.
Edit: the Exchange client I was thinking of is TouchDown, now owned (and EOLed) by Symantec but I believe originally from NitroDesk.
