The point is that under a subscription model these developers would be able to provide you with ongoing updates and quality service, w/out having to surrender to Google.
How many ongoing updates do you want from an email client? I don't know about you, but I want a pretty consistent experience when dealing with email; email is a chore more than a pleasure after all. And I don't exactly want to dish out $5/month for bug fixes. What is the value-add for the end user here?
> How many ongoing updates do you want from an email client?
Because of Spam? Perhaps indefinite. Because of new file types? New authentication schemes? New mobile platforms? New user interface technology? Perhaps indefinite.