Plenty of other industries work this way, including several branches of retail (which is a very large space). Do you ask for money back when the gas station drops prices? What about when milk or cereal go on sale at the grocery? Pre-paid hotel rooms offer no refund/adjustment if the price drops (and this almost just happened to me at a Hilton in New Orleans). You can't renegotiate the price on a car after you sign the contract, nor on shares of stock.

Retail has limits on it, for the most part. Most stores have a limit on how long you can wait before you can no longer claim the credit.

Come companies have restrictions and some don't. That's the nature of any competitive industry. I don't consider that aspect of the ticket price to be a significant inducement of my purchasing power because I rarely see a situation where it would be something I could actually benefit from (ie I generally buy at the low point anyways).