I think this is slightly dramatic. National specifically offers a "drop and go" service where you don't have to wait around for the receipt. I never wait and almost always get the receipt before I get on the shuttle bus/train.

In the one or two times I didn't get the receipt a simple phone call to the 800# or local station and they check the car in and issue the receipt.

The one "extreme" outlier I had was at SFO where they couldn't find the car on the lot. I simply gave the manager the approximate time I returned the car and he checked the tapes. Eventually they found the car and I got my receipt, maybe 5 or 6 days later. In the interim I was even able to rent a car at the same station the next week.