The idea would work well, but I know something very similar. I am very big in the jailbreak scene for the iDevice, and Apple sort of does the same thing to stop you from downgrading your device to make it easier to break out of jail.
Below is the specifics of how they do it, skip it if you don't want it.
This is where it merges with your idea. That "code" is basically the unique ECID, and the email address/ save games are basically apples verification. Of course the perfect DRM would have to find a way to make it impossible to capture that code and make the game not run unless it could connect to the server.
However, we all know that this WOULD work, so long as you had connection to the internet. That is the best idea I can come up with, maybe someone could go on a littler further?
Below is the specifics of how they do it, skip it if you don't want it.
What they do is they look at your devices ECID (custom to your device and firmware only) to tell whether you are currently running the latest version. If you are not, then you can't do anything, however some geniuses found a way to capture your ECID, and either a) you can change a few files in your host file so when iTunes asks whether the ECID is valid, it goes to a jailbreaker guy named saurik who approves it. Or b) you can run that server yourself and say it is valid every time.
This is where it merges with your idea. That "code" is basically the unique ECID, and the email address/ save games are basically apples verification. Of course the perfect DRM would have to find a way to make it impossible to capture that code and make the game not run unless it could connect to the server.
However, we all know that this WOULD work, so long as you had connection to the internet. That is the best idea I can come up with, maybe someone could go on a littler further?