I'm assuming you understand the global economy. I'm assuming you understand regulations to sell a product in another countries.Canon USA, UK, etc are their own P&L centres. Why should they cross subsidise via way of a warranty an item bought from another country.
Simple answer: ONE company. ONE world. ONE global economy. Not only for Canon, companies, makers, sellers of products. But also for us, buyers, customers.
We don't tell Canon in what countries to manufacture their products. Canon is in no position to tell us, their customers, where to buy their products - as long as they come from their factories. They should be grateful when we spend our money on their products rather than on those from competitors. It would be in Canon's own best interest to keep us, their customers as happy as they possibly can. That includes the very best aftersales service they can possible pony up and offer to us. For all their products, for all their customers, no matter where we live, work and purchase Canon products.
Fair is fair.