My guess is either 1) Valve originally had a sponsorship with Pepsi to help promote the game but later the deal was dropped (probably because of the delays that happened after the leak) or 2) these were just placeholder textures before they could implement a design for the "Dr. Breen's Private Reserve" machines.

Also whenever the HL2 leak is brought up I can't help but think back to how Valve tried to trick trick the hacker/leaker into leaving his home country of Germany so he could be arrested in the States, but the guy was ultimately arrested in Germany and got a pretty heavy sentence since not only did he break intellectual property laws, he also caused 250 million dollars worth of damages to Valve. In other words, don't fuck with Gaben.