As a user I don't get to choose which payment processor a developer uses.
> but this is very much an argument about how I (or someone else) should appreciate your business in whatever form it comes to me, and that's not true. You'll probably want point releases and features and customer support, but for 30% less than a sustainable price.
You're ignoring the higher likelihood of purchase via the MAS. When I can just click and its purchased without hassle, without issues, you have to deal with a lot less lost sales due to hard/troublesome/scary payment processes.
If you don't want to sell on the MAS, thats absolutely your choice as a developer, but you need to recognise that the MAS is a much better experience for buyers than pretty much any other option currently in use. The best case scenario is a seller who has an easy buying workflow, actually handles security correctly, uses a reliable payment processor, and gives me the required licensing information instantly.
I've not seen that very often, and even when I do, I'm still left having to manage my license information so I can easily re-install.
Also, I like the MAS even less after learning about this kind of terrible control.
> "70% of $40 is less than 100% of $0?"
This is a terrible, terrible argument for being shoehorned into giving up 30% of your revenue. Stripe (et. al) charge, say, $0.30 + 3%. Add in binary hosting fees and we're at 30%? Again, I understand the CC argument, but this is very much an argument about how I (or someone else) should appreciate your business in whatever form it comes to me, and that's not true. You'll probably want point releases and features and customer support, but for 30% less than a sustainable price.
(Note that I'm not allowed to charge 30% more on the MAS to pass on the cost... That's a violation of the MAS developer agreement.)