Alternatively, that might be the reason it converts well. It's the old game of casually hiding what exactly it is you're doing and encouraging nosy people to check it out or ask for an invite (Forrst did/does this quite well). If they showed exactly what you get once you sign up, people may be less likely to sign up if it's not what they expected. They're less likely to unsubscribe once "in" though ;-) I say "may" because this definitely doesn't work for all types of site or list but it could be the ticket here.