They're similar, but not the same. This is explained in LimeLM, directly under where you can click "Deactivate":
Deactivating a user here allows the user to activate again using the product key. The user's initial copy of your software may still be activated. Only after your software calls the IsGenuine() function will the user's initial copy of your software actually be deactivated.
To allow a user to deactivate their software, use the TurboActivate Deactivate() function within your app. See the example projects on the API page.
If you want to block users from using the key then don't deactivate any users just revoke the product key.
