Against retro music? How so? I know he's dissed Wolfmother (which was hilarious) but I've not heard him criticising retro stuff otherwise.
There was an interview he did for Faith No More just before Angel Dust was released were he stated his dislike for retro music. I believe it's on youtube.
EDIT: This probably wasn't a problem of communication my post, but I meant that he artists that make music similar to music made in previous decades, not older music.