For some businesses, the huge AWS feature set (RDS, EBS, ELB, security groups, VPC, ELB, EIPs, etc, etc, etc) is more valuable than the bottom $$ line. For others, those features aren't worth the added cost, but hand-wavey "just use DO" or "Just rent physical servers from SoftLayer/Rackspace" is disingenous.
TL;DR AWS has value above and beyond simply hour-to-hour elasticity.