But again, people haven't been denied warranty for doing their own work.

The point is, your ascertainment is wrong.

You are 100% sure of that? I have read PLENTY of stories where DIY caused warranty denial.
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In the States they have the Magnuson-Moss Warranty Act, which prevents manufacturers from denying warranty claims based on modifications or servicing the vehicle somewhere other than a dealership with OEM parts. Denial as a result of modifications isn't completely cut and dry, but denial on the basis of improper maintenance is difficult as long as you have reasonable proof i.e. receipts, odometer photos, UOA.

The Sales of Good Act is to my knowledge the closest Canadian equivalent, it's enforced at the Provincial level. I believe, like the American equivalent, it prevents manufacturers from legally denying a warranty based on servicing a vehicle somewhere other than a shop approved by a manufacturer. That's my understanding at least.