When you look at an application running on cloud resources, you need to look at all of the costs, not just the compute instance cost.
Such an analysis is highly dependent on the application. If all you need is compute instances, then Google may be a better buy.
If you need web server, database, email and DNS support, then the analysis becomes more complicated. You need to factor in system administration time.
For a startup, often an hour spent doing system administration is an hour that is not spent adding features to an application and otherwise improving customer experience.
Where Amazon Web Services shines is in the managed services they provide. These are extremely low to zero administration services. They include RDS, which is a managed database service (nderground uses RDS/Postgres). Elastic Beanstalk, a managed, scalable web server and load balancer. DynamoDB, a zero administration, zero sharding service for noSQL database support. The Simple Email System to support sending email to your customers (nderground uses this for board and photo post notifications).
Amazon’s investment in cloud services allows a startup to leverage these services and focus on development.