It comes down to what the ISP promises to customers
Wholesale or retail, if an ISP promises to supply an individual or company a certain amount of bandwidth without constraint, then that is precisely what they should supply. On the other hand, if they promise to supply a line with a specified maximum bandwidth, on a flat rate basis but with a warning about fair usage , not exceeeding a monthly limit and so on - then they can throttle or otherwise constrain the traffic.
I guess TekSavvy are miffed because they thought they were buying a service which would not be throttled. As Bell Canada seemed to change their story with TekSavvy, maybe they also believed this to be the case. I guess a bunch of lawyers will decide...