Also, as the cameras all originate from the same factory and are sold by the same manufacturer, I fail to see why the warranty would be different.
FWIW, Canon's warranties are underwritten by each country/regional divisions, which are each separate companies. Each of the Canon companies in each country set their sales and profit targets, based on the goods
that they sell and support.
Canon UK buy from Canon Japan and set an SRP and their wholesale pricing based on their expectations of the number of warranty repairs that they expect to arise from products that they sell in the UK.
Canon Hong Kong will do similar and set appropriate pricing for their market, but the costs of labour and taxes, etc. in Hong Kong are (almost certainly) considerably lower than those in the UK.
When you buy from Hong Kong, the cost of a repair in the UK was never factored into the price that Canon Hong Kong sold it at.
Clearly, Canon UK do not want to encourage people to buy Canon cameras and lenses and bodies from abroad, yet still have to service and support them, as it hits their bottom line. Warranty terms are one tool they have to encourage you to buy from Canon UK and dissuade you from buying abroad.
EU single market legislation means that warranties for Canon products sold in Germany must be honoured in the UK, and vice versa, but no such legislation exists to compel companies to honour a warranty on goods bought from Canon HK.
In the past, Canon offered a worldwide warranty on their L lenses (but not camera bodies, nor consumer lenses). Presumably, either the costs of warranty repairs were either recharged between the various divisions of Canon, or (possibly more likely) simply absorbed by the local company that actually performed the repair.
However, that policy was changed several years ago, probably as a result of the wider trend of people buying from retail channels in markets outside their own country.