Currently, any installed/enabled extension is treated as enabled extension in admin. This is done on purpose to allow access to controllers even if extension is set to status OFF. In over words, this allows user to still edit custom extension settings or access pages with extension related data.
For instance, In case of payment extensions, you still what to see payment history even if extension is disabled and no longer available in a storefront.
Regarding you question. We are looking into solution that will be logical in 1.2.3.
I will update.