With TiVo, the lifetime sub stays with the box. If you sell it on ebay, the auction winner will get the lifetime sub for example. Check ebay, boxen with lifetime sub sell for much more.

From the FAQ on tivo.com:

A product lifetime subscription to the TiVo service covers the life of the recorder or receiver you buy - not the life of the subscriber. The Product lifetime subscription accompanies the product in case of ownership transfer. The subscription remains in effect even if you upgrade your recorder, for example, to increase storage capacity (please contact an authorized dealer or the manufacturer) or if the recorder needs to be repaired or replaced due to a malfunction (see manufacturer warranty details). Because a Product lifetime subscription is linked to a particular recorder, it cannot be transferred to any other recorder (unless the recorder is replaced due to a malfunction covered by the manufacturer's warranty). Each recorder purchased requires its own service subscription and activation.
Of course, hardware products don't last forever and their lifespan will vary. TiVo makes no representations or warranties as to the expected lifetime of the product aside from the manufacturer's warranty.