Bingo. This is why we use them. EC2's performance is not great, and the pricing is only "good" if you reserve instances on a 3-year term. However, their full suite of services are wonderful. We're not really vendor locked in, either, because of how we designed our app.
We're willing to pay a premium in order to not have to administer parts of our stack. For example, Simple Email Service is so cheap and beats the heck out of running a mail server. We have 0 media servers, because S3/CloudFront do it wonderfully. We don't need a front-facing proxy EC2 instance, because ELB works great for our purposes. Background tasks are scheduled with SQS, so we don't need RabbitMQ or ZeroMQ. Auto-scaling shapes our server fleet automagically to our traffic.
Point of all of this is, you spend a ton more on salaries. We've been able to put off hiring because of Amazon's full suite of offerings, which is a huge win for us.