"Some of this risk is ameliorated by using open or popular standards and systems."
This seems to be the middle ground. Making well-reasoned decisions about which vendors will have a long and well-maintained life of service at the expense of it being trendy or cool.
You're painting as if the only risk was them going away, but there are other risks with being tied to a single provider - like getting huge price increases: https://news.ycombinator.com/item?id=2533416
Meanwhile, the original post you replied to did not say to completely avoid AWS, only to use "standard EC2/S3 services" rather than provider-specific ones. It may not be the middle point you prefer, but it's hardly an extremist position worthy of ridicule.
GAE came out and people immediately built their entire businesses on them.
It's important to provide a detailed analysis weighing the pros vs cons of building an application on any brand new service like GAE etc.
For instance, one con could've been "if they ever increase their prices by X amount, then we're fucked" would've been a pretty relevant con to consider before jumping into using it.
This seems to be the middle ground. Making well-reasoned decisions about which vendors will have a long and well-maintained life of service at the expense of it being trendy or cool.