I've only bought a handful of WSO's, and never signed up for a mailing list, so I was wondering if this a fairly common occurrence? I guess I made the assumption that, since they are advertised on the forum, this sort of thing wouldn't occur. Obviously, though, there is no way to for the forum to check for this sort of thing, so I should have known better. Lesson learned and no more assumptions.
BTW, for those with Gmail addresses that might not be aware of this feature:
Gmail lets you embed random text to your email address using the ‘+’ sign. So to make sure that your subscription with that news site you wanted access to isn't flooding your inbox with spam, register instead with "JohnDoe+newssite @ gmail.com."
Then if you get spam with that address on it, you know who sold you out.