It seems inconceivable that Ruffalo won't be voicing the Hulk since he's doing everything else, particularly the performance side of things. If he puts certain emotion into a scene, then if Lou overdubs this, will he be able to match that emotion or the subtle nuances? Lou isn't exactly known for his acting skills. Ruffalo's voice can easily be changed with technology to sound Hulk like. I can't see the need at all for Lou to step in, apart from the nostalgia factor. But that would be like getting Henry Cavill for Superman, and then overdubbing his voice with Christopher Reeve (if he were still alive and well) just because Reeve is so associated with the character.
I know that Lou was previously rumoured to be up for the voice part, but is he mistaken, or has he actually confirmed that he is indeed voicing Hulk? Look at what the quote says:
Friday during Chicago Comicon I went to an intimate Q&A session with Lou Ferrigno.
I [the interviewer]
knew he was voicing the Hulk in the new Avengers movie, and
I wanted to know how big of a role the Hulk would have in the new movie.
The interviewer says "I knew he was voicing the Hulk", but is this an assumption on his part, based on a previous rumour or old facts?
Lou doesn't say specifically he is voicing the Hulk:
Heres what he [Lou] said: I think the Hulk is going to have a major role, and I think that role will spinoff into the television series. The executive producer for Thor and The Avengers is the same producer for the Hulk television series, and that isnt a coincidence.
Lou only addresses the question of how big a role Hulk will have in the movie. Did the interviewer even ask Lou about whether he's voicing the character, or did he make an assumption and not bother to ask, and then wrote his assumption into his article as if it were fact?
Or maybe Lou still thinks he's voicing Hulk, just because he was told that at the beginning before Ruffalo was even onboard or they decided to create the Hulk via this method. Or maybe Lou thinks he's doing the voice just because he's done it every other time, and naturally assumes it will still be the case.