It depends on the policy that the developer has implemented and the licensing verification method they use. Most will use the android Licensing Verification Library, which goes through google. But some use their own method of verifying licenses, where the license is locked to a particular device by the IMIE for example. Applications that give you a KEY instead of downloading a full paid version will be using their own licensing check and will probably be locked to a device.
Some light reading:
Application Licensing | Android Developers