I also work closely with school IT in Canada. This is a common thing.
When I read the summary I was thinking "Really?". This is the school's network. Politics is very much a big part of this. People want to bring their own devices, but all the soccer moms out there want "OMG PRON" blocked 100%. To a degree I agree with this - there's a time and place for everything. School ain't the time for that sort of thing, and IT can get in some real legal hot water if they don't do something about it.
Case in point, when google implemented SSL, we found that google's image search would hand out porn happily when asked. We had no choice but to implement something that will filter these things. Moreover, as previously mentioned it's also used to dole out wireless access seamlessly.
Really, in my opinion this boils down to respect. This is an institution's network. A bit like visiting someone's house. You know the rules, and this is not YOUR network. They're letting you USE it in order to (in this case) learn. Not to look at porn (or whatever). Bring your own device? Then it's subject to the same rules.
There's nothing nefarious here.