The airline is limiting their liability. If the person boards on a 1 way ticket and is found to be inadmissible at the port of entry, then the airline is on the hook for the return fare. Many airlines will not allow travel on 1 way tickets for this reason, and they are within their rights to do so.
The whole point of Work Permits, Visitor Records and Study permits is that they are TEMPORARY, so it is expected that the foreign national will depart at some point.
It appears that the best thing to do is buy a refundable return ticket, thanx for the info by the way.