<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Originally posted by anonplz:
Why is flying to Montreal, per mile, more than six times as expensive as flying to London??</font>
Market forces. Supply and Demand.
Additionally, you're looking at a single fare with no idea what percentage of the seats on those routes go for that price. For a realistic comparison you need to compare yield (average fare paid per mile) for each route. As you know, the average often varies significantly from any single data point.