Or, if you use AWS as your only platform, accept that shit will happen from time to time. Unless your application is a matter of life and death, or unless billions of dollars are at stake, a little downtime now and then probably isn't that big a deal. (All my sites went down when Heroku did (including railstutorial.org, which pays my bills), but the losses are acceptable given the convenience of not having to run my own servers.)
I think it's reasonable to escalate criticism of Heroku for remaining in a single AZ. They have had plenty of time and resources to fix this, and haven't, despite being quite competent. I don't know if it is that they don't think it's necessary (due to the profile of their current customers) or what, but I wouldn't use Heroku for anything as long as they remain in a single AZ, and would be really reluctant to advise other people to do so. I obviously really like the Heroku team and product and would love to use them otherwise.
It wouldn't even need to be true seamless failover across AZs right away -- just offering a us-west and us-east Heroku would be enough for me, with shared nothing (maybe billing, or not even that), and then figure out redundancy yourself inside your app. Multiple regions is WAY better than multiple AZs within a region, too -- both for reliability and for locality.
Obviously a real seamless multi AZ/multi region solution would be much more technically impressive, useful to users, and Heroku-like, but they shouldn't let the perfect be the enemy of the good here.