Apps have existed with subscriptions long before now. I suspect you will still be able to buy a flashlight app for a fixed price, but maybe you'll subscribe to Hulu through Apple rather than Hulu's backend.
What's new is for someone who makes a Twitter client to be able to say "You can buy TweetMaster17000, but it's a subscription that totals $6 a year. That way I can afford to continually update it for existing users."
That's not a bad thing, but it may be a hard sell to many users.
This is part of the time-honored business model for places like fitness clubs.