Is it not more like you can't outsource customer support and product development, but you'd better outsource everything else if it's economically viable? Thus

Is it not more like you can't outsource customer support and product development, but you'd better outsource everything else if it's economically viable? Thus if your product is some kind of hosting (i.e. blog or image hosting), the reliability is your product, so you don't outsource sysops, but if you offer some project management software... Well it's almost certainly hosted so reliability is your product again and you better have your own sysops. So the only viable conclusion seems like you limit your trust to the PaaS provider and have some plan for the rare case when they get screwed. Or you could bet on technology not requiring such monstrous resources as Rails and host your entire MegaCorp on a single server rack.