What you're saying may apply to simple SaaS companies who might build a two-tier application that can be easily scaled up and down by adding front-end nodes and

What you're saying may apply to simple SaaS companies who might build a two-tier application that can be easily scaled up and down by adding front-end nodes and r/o database nodes, but it doesn't always apply to data analysis companies like Moz, who may use large ElasticSearch clusters that don't autoscale. I run technical operations for such a company. The vast majority of our infrastructure remains static, simply because the underlying technologies don't allow for autoscale. The best place for a company like ours is in a private cloud, be it at Rackspace, SoftLayer, or in colocation.