Well, increased end user speed without upgrading the portions of your network that are congested at peak times will increase the frequency of those routers actually being congested at peak times.
Either way, as data use grows Shaw will need to upgrade it's network. The question behind the addition of UBB is: are the capital costs of upgrading their network equipment greater now than they have been in the past. I'm sure Shaw has had to upgrade their gear in the past as they transitioned from offering a 5mbps service to offering DOCSIS 3 today. Has the rate of bandwidth use increased more dramatically in recent years? Did network gear get more expensive?
I don't know specifically what equipment they buy, but I imagine the price points for their network equipment probably will stay the same or (if anything) get cheaper; while at the same time becoming much more capable at enabling more network capacity. Just like everything else in computing.
So, in my mind these sorts of speed upgrades fit with the rate of "bandwidth inflation" that the internet experiences every year. This is a good thing because it is required as users consume more data, and it isn't justification for or against UBB.