Most Google Music users will never know it, but there is a limit to the number of devices that can be authorized and associated with a single Google Music account. Specifically, only 10 different ROMs may be authorized. This limit was never a problem for ordinary users. For edge cases, such as tech journalists who review many phones, a simple, if roundabout, solution was to de-authorize old phones or ROMs in the Google Music settings.
Now, however, the hackers over at the XDA Developer forums have discovered there is a new limit to the number of devices that can be de-authorized. User Amphibliam on the XDA Galaxy Nexus forum revealed that Google is now preventing the de-authorization of more than 4 devices per year for each Google Music account. The smartphone users in the XDA community often root their Android phones and flash them to an updated ROM frequently, meaning this new limit prevents them from experimenting with their phones as much as they would prefer.
There is no word yet on why Google has implemented this limit. It really only affects three very specific types of users: the aforementioned tech reviewers, the Android modding community, and Android app developers, who must test their products on a wide variety of phones to ensure compatibility. These are precisely the users that Google does not want becoming unhappy with its services.
(XDA-Developers via Slash Gear)