I wouldn't call that a "subliminal" message. Just like "1984" and every other dystopian science-fiction story ever written, "The Hunger Games" acts as a cautionary tale of where our society could go if we're not careful. It makes a very deliberate connection between our current "reality"-hungry society and the Roman gladiatorial games of the past. That's not a secret and it's really not so sneaky as to be categorized as subliminal. You've simply discovered one of the story's many themes/messages. All stories are built on a theme or central idea of some sort and science fiction/fantasy, in particular, will often use metaphors or futuristic settings to comment on present-day issues. But, it's not meant to be hidden. It's simply a metaphor that you're supposed to notice and think about (and look, you're already doing it!). Subliminal would imply they're trying to brainwash you and that's not the intention. You can't think about the message if you don't consciously make the connection. ;) Stories set in the future are always built on what's going on in the present. So, yes, I'd say "The Hunger Games" is, definitely, a commentary on where our society could be headed but, I don't think it's meant to be written in stone. It's simply a pointed and intriguing "what if".