Kingston has some very real social justice problems, a worrisome unemployment rate, poor physical infrastructure, and an inadequate industrial tax base. I imagine this ranking reflects only those who fall around or above the reported average annual family income of $67,000, which is surely not a fair snapshot of the city's socio-economic reality.
It would have been much more accurate to report the overall median Kingston household income, which the 2001 Canadian Census reveals was $58,413. That's a significant variance from the average! However, single-parent households (which the Census reports were 15% of Kingston's population in 2001) fared worse, with a median income of $29,872. Surely these latter households do not have 24% discretionary income as reported in the ranking.
The city has an unusually high concentration of public service institutions (Corrections, CFB, Queen's, RMC...) whose employees stack the income data on the high end. My understanding is that we have a very high proportion of citizens on social assistance, many of whom are the families of those incarcerated in the region's plentiful correctional (i.e. prison) facilities.
So I have mixed feelings on this ranking. In many ways I am proud, as this is my chosen hometown. I have made this my home for some 16 years, and I have certainly come to agree that my quality of life is higher than my friends and peers in other cities. But we fail all of our citizens if we sweep the realities of our disadvantaged off the street with another glossy ranking.