Hi Nomad, that's an interesting question.
In my opinion, such rules would put a dent in entrepreneurship and therefore they should not exist. Just because I happen to live in Canada, I think it would be unfair to deny me the freedom of purchasing other country specific domains such as .in, .be and .us.
Also, where would you draw the line with such restrictions? I am originally from the UK, so does that mean I would be eligible to buy both .ca and .uk domains?
I'd be interested in hearing your views about such restrictions.