Most traditional platforms require a plugin to handle subscription billing, and that's just one part of running a subscription business - when each new need you have requires a new plugin, you'll end up with what we call Plugin Soup.
To recreate Subbly's functionality with other platforms, you'd need to hack together a wide range of plugins.
We are not against plugins, but we firmly believe that anything business-critical shouldn't be powered by a plugin.
You're only as good as your worst plugin after all.
all your current customers quickly, painlessly, and for free.