30% Net isn't that crazy. Median household income is around $98K (before the crash). Should net around $80K (based on 2 incomes).
30% of 80 is $24K or $2k/month. That should service a $400K mortgage (or a pretty good detached home).
Calgary Median detach price is $503K. 20% down yields a $400K mortgage, all numbers make sense.
And if you try the TD Affordability calculator, they will even push you to $550K house with these numbers.