The argument in your last paragraph is almost exactly what everyone said about Apple's approach to subscriptions. "Apple would be crazy to demand 30% from publishers and distributors. Amazon can't afford 30%!"
Yet here we are today, wondering just how the hell everyone is going to carve 30% out of their business model. Anyone who thinks that task is anything even approaching trivial has never run a business.
I wasn't arguing that Apple won't do it, just that they would be even more crazy to try this for SaaS than for content subscriptions. It's one thing to charge 30% for when someone is selling an entire product through your platform.
It would be unprecedented if they tried to charge 30% merely for access from your iOS device to a SaaS app. I think there is a pretty big difference.
Lastly, carving 30% out from your list price is pretty common if you're the wholesaler, manufacturer or orignal producer. For most of those scenarios they'll often be able to afford much more than 30%. It's the middlemen and distributors that get really hosed...and unfortunately services that do provide value but licence their content from others are collateral damage.
Yet here we are today, wondering just how the hell everyone is going to carve 30% out of their business model. Anyone who thinks that task is anything even approaching trivial has never run a business.