I can't find any reason why obito want revenge of his clan on the uchiha massacre.. Any ideas?? But at this moment writing this.. I thought about obito was telling itachi that he is madara.. So maybe obito said those words about the revenge because the uchiha clan has betrayed madara..
I don't remember exactly that well anymore, but Obito I know he impersonated Madara. Madara has left the leaf village. In episode 345 or episode 346 of Naruto Shippuuden it was already shown that Obito was "supposedly Madara". Madara then spoke through Obito and it was later said that Madara Uchiha was manipulating Obito. Maybe that's what this is about :)