As a relatively fragile portable device with a limited-life sealed battery, which is essential to people who adopt it, there is a nice replacement market. Being

As a relatively fragile portable device with a limited-life sealed battery, which is essential to people who adopt it, there is a nice replacement market. Being nice to your users by providing relative low-cost maintenance software updates should more than pay for itself. No need to include new features, they can be sold for a one-off optional fee to old device users. Subscription is worse here: it provides weaker feedback from users to the developers, who have a harder time knowing if the new features are useless or damaging to the user experience. Products don't always benefit from constant gratuitous updates.