Do you think for the foreseeable future Groot will be only able to say "I AM GROOT!" ? It seems like that's become an iconic part of the character. While I do enjoy that aspect of the character, I do miss his characterization by Giffen.
On the other hand, in his original appearance in TALES TO ASTONISH, he was as verbose as any other of the pre-hero Marvel monsters. So perhaps he chooses not to speak.