Courtney Love and Dave Grohl love money more than their dead husband and bandmate, so Love let Activision include his image and Grohl let them use his music in Guitar Hero, where people make him sing Bon Jovi songs.

UPDATE: This post has been edited to reflect the fact that, while Grohl and former Nirvana bass player Krist Novoselic licensed the rights to use Nirvana's music for Guitar Hero, they don't have any control over his image. You can read their statement on the matter here.