One of the Italian journalists (caveat emptor) spoke to Simoncelli, and Simoncelli told him it had come up. That journalist (sadly, I wasn't paying close enough attention during the Italian-language debriefs to notice) then started asking everyone about it, and so they got quotes from all the riders. As I understand it (but this is mainly journo gossip) it was Rossi and Simoncelli who brought it up in the Safety Commission.
He is, it's just that his statements on the issue were so bland that nobody bothered posting them. I have audio of him which I haven't transcribed, but it was mainly "yes lighter riders have an advantage in some points, no, I'm not sure what we can do about it." Stoner was much more quotable on the issue ("This why I don't go to the Safety Commission any more. They only listen to certain people, and they don't talk about safety. What's the weight issue got to do with safety?") hence his quotes appeared in all the publications.
I should also add that journalists tend to goad Stoner into making comments, because he provides such fantastic quotes. If you can get him when he's annoyed about something, and send him off on a subject (whether related or not) you've got your headline quotes for the weekend. It's fast and easy journalism. Rossi understands the way the press works much better, and is much more selective in providing a juicy quote, choosing his time and place more carefully.