It may not be a %-age of revenue, but you definitely can't host a non-trivial webapp for free either.
You could even argue that in many webapps scaling costs are proportional to revenue, which makes it awfully similar to an app store.
> But also I think there's a false dichotomy between "the Web should just be for documents" and "the Web should just be for apps."
Yeah, I don't have a clear idea on where the web should "end", but wow... web pages able to eat all my cores and have data races seems like a line to be crossed with great caution and care.