Well the bookshelf analogy isn't perfect either because a bookshelf serves no purpose without books while most normal people just use the built-in apps plus a couple more.
Also book authors would be really excited about paying only 30% to have a shelf maker distribute their book because they currently pay about 90% to the publisher and retail outlet.
Yes I am saying "well feel free to not make a mobile app" and I don't think that's a ridiculous position and I'll explain why.
For a start neither Apple nor Google had to allow 3rd party apps, and actually neither developers nor government would have been able to force them to do so. However they created massive industry and that's benefited them as well as developers and users. The two are in heavy and healthy competition with each other. If they colluded to keep the cut at 30% I would agree that some government action is warranted.
The other thing is if you look back in fairly recent history you see that software developers have a pretty bad track record in terms of respecting their users. People regularly had to reinstall their operating systems to rid it of malware and crapware that was really difficult to get rid of. This situation would clearly be intolerable on phones hence all of the restrictions and app reviews.
Apple and Google also bring customers to the developers. They are providing a lot of value for developers, if the 30% was that bad then 3rd party apps on phones would have never become a thing because developers would have never made the choice to develop for them. So clearly it was a good value proposition before the market for apps exploded so it should be an even better one now.
I think your underestimating the value that Google and Apple are bringing here. They've created a marketplace where customers are really comfortable with trying free apps and buying apps and subscriptions to apps. Cancelations are simple. You've got one-click purchasing which makes it really easy to impulse buy. No one has to give their card details to random companies all over the world. Refunds are easy. It's also really easy to delete apps. Users haven't got to worry that the next update of a trendy photo app is going to install some toolbar into their web browser. All of this creates more sales of apps. I don't think it's unreasonable to take 30% of sales in exchange for this.
Finally it's not like developers can't make web apps that are compatible with smartphones. You can even save the web app as an app icon. Okay so maybe push notifications don't work but so what. The issue is that some developers seem to want it both ways. They want the benefits of the marketplace but they expect Apple/Google to provide all of that for free. It's a sense of self-entitlement I think.
Anyway thanks for the conversation I should probably go sleep now. Also I'm kind of tired of defending two of the largest companies in the world. It's not really me.