Currently in the UAE, where I have discovered that mall walking is a serious activity (The Mall of the Emirates in Dubai offers such service):
According to about.com, the advantages are:

Out of the weather: Inside a climate controlled mall, walkers can dress comfortably and not worry about wind, rain, snow, ice, heat.
Away from the traffic: No intersections to cross, broken glass or bushes obstructing the path, auto fumes or rush hour.
Security: Walking with others and with mall security on duty.
Restrooms and water: always nearby in the mall.

Walkers get a jump on other shoppers as the stores finally open in the morning, a big advantage during the holiday shopping season. No wonder mall merchants support walking programs, it ensures loyal customers who return several times a week.

Free blood pressure checks, low cost or free cholesterol screenings, presentations by health and exercise experts are other perks for mall walkers. The mall walking club may organize to take groups to charity walking events or other organized outdoor walks.

PS: The Mall of the Emirates is the one with the ski slopes: