@glockenspiel: I see what you are saying there but I don't think any of us girls are "tricking" people into joining. Sure, money is nice. But we want people who are interested in us and plan to stay with us. Just because you aren't interested in a type of person doesn't mean someone else isn't.
You also have to stop to think what other reasons there might be to not show full nudity in the free. Take me for example, I don't like to because it makes me uncomfortable. This may sound odd to you but if someone is interested in me enough to pay money to see me I don't mind showing them everything. But the idea of people just browsing my free pictures to get a good look at my naked body every time I update then not pay for anything makes me feel sleazy and used.
Also, if you don't like someone's free pictures or if you aren't sure they are good enough for your standards you can read their info on their site, email them, or just move on. There are PLENTY of Charms to choose from. If they aren't selling to you personally that's their own problem.
@timboy: Good point!