While Guitar Hero: Aerosmith hasn't had the resounding success of its counterparts, its still sold well. Its not only a success for Activision, but for Aerosmith as well:

More than half a million plastic-guitar-toting consumers took home copies of Guitar Hero: Aerosmith during the week following its release on June 29, compared with just 160,500 for Aerosmith's Honkin' on Bobo album, released in March 2004. Gross sales figures show an even more dramatic gulf: Guitar Hero: Aerosmith, at $50 a game, generated more than $25 million, while Honkin' on Bobo only managed $2 million. -- Yahoo! Games

I think anything that sells over 100,000 copies in spite of being named "Honkin' on Bobo" should still be considered a success. Maybe that's just me.