It's the same subscription, but it's easier to manage your subscription if you subscribe from the web. For example, you can easily change or cancel your subscription within the web application. For iPhone in-app purchase, you need to go to your iTunes account to cancel or change your subscription.  Also Prime Business plan is only available from the web.  Coupon code can only be used from the web. 

To subscribe from the web, please logon to our web version using the same Google account you are using on your mobile app and then click Subscription menu on the left.  Here is how the web subscription page looks like: