It won't do anything for a typical adult paysite, which has fully secured individual logins. For once-off purchases such as ebooks which redirect to a static download page (with no form of authorisation challenge) then it's obviously a problem.
Alexa isn't the only entry into these, I'm sure plenty of people share the URL so their buddies can download content too.
Imagine if adult paysites didn't have any kind of membership security, the only difference between being a member and non member was that you knew a "secret" URL to gain access?
