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.
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.
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.
It's important to ask questions like that – "what happens if this service got away / becomes unaffordable / removes features we depend on". There's risks in that sense with using proprietary technology. Sometimes it'll be worth it, because the benefits of allowing you to deal more quickly with business problems will outweigh the technical risk. But I've definitely been in more than a few situations where a vendor has shut down a product or service that I depended on, resulting in a difficult or time-consuming migration.
Some of this risk is ameliorated by using open or popular standards and systems. Intel's not likely to stop producing x86 chips; GitHub is probably going to continue supporting git; Linux isn't going anywhere anytime soon. It's worth thinking about before using a service that nobody else offers!