I work 48 - 72 hours a week depending on the needs of the week at my job and i can tell you i don't have a lot of extra spending money, but when I do buy something I buy online because its generally cheaper for a number of reasons. Id say the biggest reasons are the number of people selling and none of the costs involved in running a brick and mortar business.
I bought some electronics online for half the price of its listed price at bestbuy and doing a quick search i have found better alternatives for what i want for the same price or cheaper. online is the new way to buy (at least if its not shoes or food) but i'm sure time will solve the problem.