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.
ONE company. ONE world. ONE global economy
Really??? Even within the US a company can set up different sales offices to sell to different regions plus a national accounts sales office. Cost, P/L, bonuses are based upon local results.
By your logic, would it be okay for Canon to require you ship warranty products back to Japan (or some other global local) for servicing?
A small bit of the price of every item Canon sells goes to warranty support. If you buy a gray market item, Canon USA (or which ever local country) does not get this support. Cost reassignment will work well - for example a Canon USA tech may make $125 / hr (all in after benefits, ...) while similar position in India may get only $50/hr. If Canon USA were to rebill Canon India, at what rate? Canon India set aside only $50 / hr for the repair but Canon USA needs $125.