Yes but if you let your subscription expire to adobe you still have your pictures that can be edited in another program. You will not be able to edit your C3 games without maintaining the subscription.
See the difference?
Isn't that obvious? It uses a propriety file type.
This same limitation applies to Photoshop - sure there are other image editors than can open .psd; but none provides the true 1:1 full feature conversion that Photoshop can offer, and they fall out of date whenever new features are introduced. This isn't even getting into the fact that 3rd party software can actually break .psds, so making a file in Photoshop, saving it as a .psd, opening it in Gimp, editing it some more, saving it again, and then re-opening in Photoshop; could result in a corrupted file.
Like Adobe's products, the editor itself is one of the many services you're getting by paying the C3 subscription. As it's an going, ever improving product that's being added to - a one off payment simply doesn't make sense from a business (and some would say ethical) standpoint.
You don't begrudge Adobe for this practice? Why Scirra?
Your argument is that users need to be able to edit their games post-subscription because publisher contracts demand that games purchased must be updated regularly, this doesn't hold water for two reasons:
1) Scirra is not responsible for the business decisions of it's users.
2) I have worked in creative software development for years. I have worked with and for game publishers, including HTML5 publishers. In all that time, I have never once seen a contract that stated the need for maintenance of the product purchased that was not:
a) Compensated for in the initial purchase order.
b) Stipulated to be carried out at a set fee, often an hourly rate plus associated costs . Which in this case would be the C3 subscription.
c) Included as part of a retainer fee agreed with the developer.
Unless there has suddenly been an influx of publishers that don't play by these standards, I'd consider your case to be a rarity. At the very least I certainly wouldn't work with these publishers!