Honestly, that's pious bullshit. It's the thing people keep saying every time Heroku gets mentioned is that it'd do better than you would yourself for availability, but you'd have to be borderline incompetent to have as much downtime with a more traditional VPS / hardware hosting to match the combined Heroku / AWS downtime.
We moved all but one of our Rails apps off of Heroku precisely because of the frequent downtime -- or, rather, that was the last straw; there were other issues, notably the difficulty in debugging production issues, that had us already debating such. Heroku has gotten somewhat better, but it's still down far more than anything else that we use. (And we have services spread across Linode, Rackspace, AWS and the mentioned one app on Heroku.)
You'll have better uptime in most cases with a standard nginx / passenger setup on a $20 VPS than you will with Heroku.
Huh? The flakiness of a standard uplink will have you down for 44 hours a year? On what planet? With our non-AWS hosting providers we tend to see 2-4 hours of network issues per year. Heroku's uptime also hasn't historically been anywhere near 99.97%. They were down for several days last year in The Great AWS Failure.
I don't think anyone ever considers hosting it on a desktop in the closet on DSL at home/office.
The competition for something like Heroku is EC2, VPS, or dedicated servers, in commercial colocation facilities. A good hosting facility is going to be a lot closer to 99.995% uptime for network and power to the box, but you can of course screw up past that point on your own.
Having administered several "standard uplinks" from 100 Mbit/sec all the way to multiple ten Gbit/sec links, I can safely say that if your transit isn't 99.999%, you need new transit.
Yeah, I think Heroku is better than other options for being a fast/easy way to deploy, and great UI and some useful tools, but the combination of lack of visibility into internals for debugging, Heroku outages, and EC2 outages is the reason I don't use it for anything in production.
I'd seriously consider Heroku if they were in multiple regions (fuck AZs, those are a lie). There are huge advantages to a PaaS in terms of speed and lack of hassle, and a well run PaaS is better than most developers at operations, patching, security, etc. (We're kind of unique in that we're better at operations than development, though.)
We moved all but one of our Rails apps off of Heroku precisely because of the frequent downtime -- or, rather, that was the last straw; there were other issues, notably the difficulty in debugging production issues, that had us already debating such. Heroku has gotten somewhat better, but it's still down far more than anything else that we use. (And we have services spread across Linode, Rackspace, AWS and the mentioned one app on Heroku.)
You'll have better uptime in most cases with a standard nginx / passenger setup on a $20 VPS than you will with Heroku.