[mdaniel]

My suspicion is that they have distinct names/skus because (a) they're billed differently (b) they represent different security choices. If I grant a developer's account the ability to create "virtual router" entities, that means said developer can do all kinds of things I may not approve of. If I grant them only the ability to create "Internet gateway" entities, I know exactly what I'm getting into and (more or less) what I should expect the bill to be for that

I do agree with you that having a separate "egress-only Internet gateway" for IPv6 is dumb and confusing. I'm sure there's some number of pizzas which explains this Conway's Law instance