The version of the Google Play Services becomes an issue when there are two modules using them. For example - I'm developing a Chromecast module which must use a recent version of this library, in a project that also uses the ti.map module. The project will not build if there are two different versions of Google Play Services, thus in any case I overwrite the version in ti.map with the newest copy.
This is also true of other libraries, such as the Android support libraries. A project will not build if there are two different versions of the library in modules, Titanium, etc.
Thus, Titanium and its modules should always have the latest version of the relevant libraries - good practice in any case due to bug fixes, etc.
In most cases all that is needed is just replacing the file with the new version.