Regarding "If you are big you are paying an incredible premium to be on Heroku": Sure, Heroku is great (or cheap) for development and small-time deployment, however it is likely true that people get locked into it and (hopefully) grow quickly before they can scale away from a PaaS solution. In these cases, it is imperative to consider the marginal cost of alternative/off-site failover vs. the cost of downtime. This is what I meant by "separate the men from the boys". Those guys who are paying the incredible premium to continue to host on Heroku likely -know- that they are doing so, and have made that decision consciously.
While the situation is different, I am reminded of when AWS went down awhile back and the sites that had automated failover to alternative clouds really stood out.
The bottom line is that no one solution is ever enough. Tiny apps can likely get away with unexpected//unplanned downtime, however it ultimately delegitimizes them in the eyes of their users (read: customers), and that is universally bad.