OK let's see how much oil that would use. Let's assume the central market is about a mile away. Let's further assume you use cheap schedule 40 12" PVC piping. 12" might not be enough for all deliveries but can probably deliver 90% of the food grandma will want. That's 55,000 pounds of plastic, and that means we'll need 14,000 gallons of crude oil to make one tube to one grandma. Now, let's say grandma lives there for 20 years before she passes on, and the house gets used for 50 years before getting torn down in favor of the latest/greatest new idea for a house (and presumably a new delivery system.) That's 280 gallons a year over the life of the house. Now let's say we get her a cheap car instead, like a Yaris. One trip a week over that 1 mile will be 52x2=104 miles a year. At 35mpg that's 3 gallons of gasoline a year for groceries, which means 6 gallons of crude oil a year. How are you going to get that extra 273 gallons a year of oil for grandma? And does that make pneumatic tube grandma one of those greedy, selfish people? The devil is often in the details.