I've heard many times that it is possible to have thousands of subscribers to your newsletter even if you don't have a website/blog. What do you guys think? I've been searching through ezines and still can't figure it out.

You can partner up with related sites which do offer memberships to do a co-registration. For example, part of the registration form might be something like "check this box to subscribe to XYZ mailing list". You would negotiate a payment with these sites based on how many subscribers you collect, and in return monetize your mailing list by selling advertising in your newsletter.