The second I opened C3 in a browser I was amazed. C3 is so revolutionary. It's worth the subscription.
On that note, subscriptions as a business model are tough to sell. People have to be fanatical about the product in order to pay a monthly subscription. Subscriptions are easier to sell in a B2B setting. B2C settings are tougher.
Personally, I like subscriptions better because I get updates all of the time. Scirra has to do work so they should get continually paid for it.