As I've said numerous times on this forum, Apple is in business to make money not give stuff away for free. 30% is not bad at all when you consider that the developer is getting 70%. What other medium could a developer get that kind of a deal?
If they chose to sell the app themselves on their own website they would still incur expenses in getting the word out and getting people to download their app. I'm guessing that would amount to costing a lot more than 30% of the revenue on the app.
The developer gets diddly squat from Apple on subscriptions (as far as value / services provided goes). Apple isn't doing anything that the developer couldn't do for pennies vs all of the overhead the developer has.