Forever seems like a stretch. When Switch is succeeded, how long before Nintendo shuts the Switch shop down? You can't legally move downloaded games between consoles.
This was a big issue with WiiWare when Nintendo shut down the Wii Shop. People could keep what they had downloaded, but once the Shop shut down, you couldn't redownload anything.
Download is only one way to buy Switch games, and at least I'll still be able to use one console - compared to zero as soon as I stop paying my feudal obligations to Apple.
And almost every game available on cartridge has some kind of patch only downloadable from the store. Some don't even have all their data on the cartridge and need a download to function at all...