[Quoth]

What happens if you get the app licensed and then later you have no internet or the licence server is gone?

Or you need to install the app on a replacement tablet / phone. I've one paid app and it somehow is the paid version if I reinstall on a new phone from the same account on the Google Playstore, but the demo version if installed using a different Google account.

However I'm not ever again giving Google a payment method, so no more Playstore paid apps or Google Playbooks that aren't free (In contrast you need a working payment method on Amazon to download a free ebook, gift balance used to work).