Jeff:
Most of these sites have open subscription forms, which invites abuse. If they have any kind of incentive programs for "affiliates" or anything like that, then that plus open subscriptions would *beg* for abuse.
I've seen this phenomenon before... but I don't think this is at all what is going on with quickinspirations. The volume of (illegitimate) subscribers seens too high... but I could be wrong.
Where I've seen open subscription forms really get abused is where you have a political web site where someone signs up their friend/relative (without their knowledge) and that friend's politics differs... so that they can "teach" this person. Or a political enemy of the web site signs tons of people up anonymously just to get them in trouble for spamming. In fact, I recently got wnd.com (whose newsletter is "open loop") off of spamcop for this very reason, and they are ranked 1,595 on alexa.com!