Saying that the connection is technically capable of 20Mbit/s is different from guaranteeing 20Mbit/s in any possible usage situation. The problem with my analogy is that people generally have an idea that you can't go faster than maybe 80mph regardless of what car you have, but there is no way to know if the "up to 20Mbit/s" connection means actual usage will show 15, 5, or 1... So yeah, they should somehow be required to tell you, at least at signup, what the typical throughput on your connection will be.