The info about vending machines in GTA V is not quite correct.
1. Vending machines do have unlimited supply, but they need to be "refilled" after purchasing 10 cans in a row. I don't know yet how much time has to pass and/or how far you have to get away for a vending machine to be restocked, though.
2. Drinks you buy from vending machines instantly heal players back to 100% and not just a portion of their health, making the vending machines very useful.
3. The player character always buys a can of Sprunk, regardless of whether using a Sprunk vending machine or an eCola machine.