Forgive the side-strafing,
to be honest we all understand your problem,
forgoing the analogies and the bits vs bytes,
I'm sure you're actually getting 4.5Mbit vs expected 20Mbit.
This story is as old as Shaw,
and really beside the perpetual CSR-Support-TechnicianToHouse-Repeat, you've already went beyond by submitting the averages for your town.
So to acknowledge your concern:
YES, Shaw continually collects service fees for service that they advertise to have a certain amount of speed per second, yet in reality the service delivered is not up to advertised speeds.
NO, they do not proactively offer refunds, nor do they monitor each individual account for the performance.
YES, it is outrageous and deceptive.
NO, you are not the only one.
NO, this is not new.
YES, Shaw has given refunds and prorated adjustments on per-case basis.
The whole situation is location-specific, and in the end, you have to consider what is available to you locally, and if 4.51Mbits is the highest speed offered in Nelson (by Shaw), then that is what you will get. It is your responsibility to adjust your Internet plans according to the area - and NO it's not supposed to be - but it is what it is