If you have 100 subscribers that ALWAYS comment on stories before they reach the main page... what happens?
Nonsubscribers will have to sit under all the subscriber comments, because they will be modded up before the story even hits the frontpage.
What does this mean?
Most non-subscribers will leave, or just become readers and not comment (why comment if you never get 'heard'?).
Someone gets a subscription, then posts the story as soon as it hits the 'future' queue into his/her own website. So you'll be stealing stories from