I'm sure glass is far more environmentally sound, but to claim that glass production, glass cleaning(and the harsh chemicals and their production cost to the environment), and water for flushing afterwards are not relevant, would be wrong.

So every business off-loads some environmental impact to the tax payer.

My point? While your statement is true, it has nothing to do with how the business decision is made re: cost to the business. The metric used there is "what saves the business money".