Maybe it's because I used to work in hospitality, but this line of questioning comes across as blaming the employee for things they didn't do. The rental employee doesn't check out the mechanical functions of every car before giving it to the customer. And the hotel Front Desk agent didn't design how the mobile check-in function interfaces with Starwood systems.

As mahasamatman notes, you're putting the employee in a no-win situation. If she or he says, "Yes, it's pointless to have mobile check-in if you also have to wait in line," that's effectively disparaging Starwood. While you may appreciate the candor, other people would find it off-putting for an employee to say negative things about their employer in front of a guest.

You were upset. I get that and it seems appropriate. But, expecting an hourly employee to accept responsibility for poor implementation of a product by disparaging their employer is not appropriate.