There's nothing to understand with DO because they don't tell you what their definition of a "CPU" is. For all I know it could be oversubscribed in a worse way than EC2.
Most people don't care the exact speed of the CPU for a server, as long as it's stable and doesn't lockup with little load, especially when purchasing a Micro instance. If CPU utilization is high then it's time to upgrade to another CPU or start another instance if possible.
It would be better to do real speed tests of each service to determine average "CPU" speed. I'm sure both services are constantly optimizing for both shared hardware usage and speed, so the stats would have to be updated regularly.
