It's more that if you make use of the Amazon APIs for autoscaling other services, you can't just directly translate that to a more static managed hosting environment.
Probably the sane way is to special case some subset of your functionality so it works regardless, and then gracefully scale up/down your app (performance, scope of features, etc.) based on system health. This is a lot more complex, and really hard to retrofit.
From the very beginning i've always strayed far away from anything that locks us into AWS. For this reason we've made no use of anything that couldn't be picked up and moved away, so for us auto scaling was never something we decided to utilize for this exact reason.
While this held us back a bit at first, even tools like SES initially only had an API provided by Amazon. Now it supports standard SMTP connections, so we decided there was no harm in using it as we could easily make a switch with no code changes.
RackSpace has a fairly sane API for building new servers. If you're not adverse to using Ruby, the fog gem is pretty awesome when building servers for Amazon and Rackspace's Cloud.
Probably the sane way is to special case some subset of your functionality so it works regardless, and then gracefully scale up/down your app (performance, scope of features, etc.) based on system health. This is a lot more complex, and really hard to retrofit.