Ah - yes, that clarifies nicely. At the moment the Device Group device type can always be controlled (sent on/off/toggle commands) because this device type is implemented as a standard On/Off (relay) device type. For obvious reasons, we have various places where On/Off devices can be controlled easily by the user (tapping on the icon in Indigo Touch toggles, etc). Perhaps a better name for this device type is On/Off Device Group (we'll consider changing the name).
I think what you're looking for is a Sensor Device Group - in that sensor devices just show sensor values but provide no user mechanism to change. I'll add that to the feature request list.
The easiest workaround is to just put the status of the group on a control page but with no associated actions to eliminate any accidental taps/clicks. And when using the other parts of the clients just avoid manually changing it...