This can't have anything to do with discouraging under age viewers, there'd be no practical point. Sexy websites don't go out of their way to discourage an underage audience, they just need to protect themselves from liability. You do that with an "enter/leave" page wherein the user electronically certifies their age, that's all you need to do. The user IS still fourteen and electronically signing the document but it indemnify the site. There'd be no practical legal reason to have a separate clothed/nude/xxx portal system and no obvious benefit financially from a system of model organization based on these three criteria (unless you were actually promoting fully clothed camming but that seems really unlikely)
Reasons you WOULD implement a clothed/nude/xxx category system:
(it's tinfoil hat time)
If I'm doing a countdown and am nude but not playing I have a few thousand people in my room. If I hit my countdown target and flip the XXX switch it kicks all guests and basics out. They angrily verify their age with a credit card and become a premium. Other sites employ this as well, you get a great big "YOUR CREDIT CARD WILL NOT BE CHARGED UNLESS YOU CHOOSE TO BUY TOKENS, AGE VERIFICATION IS 100% FREE" and you sign up to view the show. It's a fucking genius marketing ploy. There will be those who verify their age and never buy tokens but MFC is banking on token trigger fingers once they get the user so close to having token buying power. I think it's an organizational response to all the hardcore public shows. Seeing 5000 people in a room for a public show and noting that only a dozen or so are tipping would alarm me as a business person, my solution to that phenomenon would be to create a system that encourages the silent lurkers who honestly don't even NEED to buy tokens on this site anymore and just full penetration channel surf to register their credit cards with my site. They don't HAVE to buy tokens, but they're vastly more likely to if they've registered their CC info.
What would they do if I registered myself as XXX but then didn't spread in public? So now as opposed to worrying that I'll get fined or suspended for fisting in public I'll get fined or suspended for NOT fisting in public? I would absolutely check the XXX box because that's where the majority of traffic would be headed, but you can't MAKE me penetrate in public, you can't MAKE me be nude, so what the hell is your recourse if I'm falsely advertizing myself? If I get caught wearing clothes do you banish me to the non-nude section? I make MFC an assload of money, it would make no sense for them to limit my exposure to the clientele by bumping me to the "bitch iz no fun and sez she won't DP in public for less than $500" page.
I feel like we're all bewildered bushmen standing around a glass coke bottle that fell from the sky wondering, "WHAT DOES IT MEAN??? What are the Gods trying to TELL US?" lol