This is only true with the small instance type though, which is severely CPU handicapped. The larger instances (> medium) get the full CPU throughput. Their "EC2 Compute Unit" rating is mostly marketing, I could never verify it by practice. Some instances with twice the ECU actually give more than twofold performance, while instances with 1 ECU should be renamed to 0,25 ECU.
I would expect anyone who works with AWS to know this by now.