Future generations may view indoor retail centers with as much suspicion as rotary telephones. These erstwhile teenage hangouts are suffering 40 percent vacancy rates and appear to be on the way out. While the obvious culprit is Internet shopping, data suggests that less than 10 percent of retail sales take place online. But that statistic includes grocery and car dealership trade, and when stripped of food and automotive sales, the Internet figures soar. Shoppers reaching for the mouse rather than the car keys really are killing American malls.