You're assuming what you see (eg lack of capcha) is all the protection that exists, and that there's no other protection. It's kind of like Disneyland - a lot of work goes into making the site what it is, and you don't see even a tenth of the work that goes on into making it look so good.
What could possibly go wrong on a site where getting an account doesn't even require a pulse. I'm pretty sure I didn't have to fill out a captcha.