No, they really aren't. I work on a top 20 machine, and can tell you that attaching this via a high-latency interconnect (read: the web) would completely kill the purpose of using this machine. And no, you cannot just "compensate by using more nodes." Amdahl's law kills that idea right out.
I've worked in both "cloud computing" (back when it was known as "grid computing") and HPC or High-Performance Computing. While they are similar in some ways, they are designed to fulfill different purposes and are best suited to different job types. The codes being run by Cycle for this project are EP codes, ones that would not necessarily benefit from the top 50 machines in the world. These machines are better suited for MPP work, which depends more on low-latency, high-speed interconnects.