Isn't the canonical answer to these kinds of questions that you're missing the sales tax that would inevitably be added on to the US/Canada prices?

Although, having said that, checking Quebec[1] gives me CAD803 which is ~GBP443 -- ~GBP150 lower than Amazon's UK price of GBP599.99

[1] http://helpsme.com/tools/free-gst-hst-pst-sales-tax-calculat...