The desktop verson allows you to check for updates of the desktop version
The desktop version allows you to show the registration info of both versions
So why does the desktop version not allow you to check for updates of the Mobile version ?
(Based on the fact your registration the desktop version should know you have a mobile version)
(Based on the fact you sync to mobile the desktop version should be able to work out the CURRENT mobile version)

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The mobile version could also have a check for updates version.
(as many devices have internet over wifi or gprs)