I think that is a little unfair. The physical rack structure generally provides two things, a networking switch and power hookup, and both are two of the more reliable things that datacenters offer. In order for your application to survive a rack failure (either power cord unplugged or network switch breaking) then you need to have fully double every necessary part of your application on another rack, which is going to be pretty inconvenient.

Companies like Amazon and Google no doubt spend a lot of time thinking about the physical locations of servers and how failures might affect them in terms of uptime and data loss, but for your average small application I think it is ok to accept very small risks that will result in downtime as opposed to spending a massive effort or engineering around it.

I also appreciate that services like Heroku hand stuff like this for you, but what I'd be really interested to see is take your average dedicated machines at your average datacenter and compare the uptime to a service like Heroku. Because while dedicated machines have failure cases (power outage, networking switch breaks, one of your machines hardware dies, hosting company has networking issues, etc), AWS/Heroko have them too (AWS outage, DDOS attack against Heroku, AWS/Heroku engineer makes a mistake, etc).