Well, you say 'abnormally/irregularly slow' and 'not unheard of', but the article quote says 'often', which suggests it's frequent practice (along with the general tone of the article).
Scheduling is quite open to abuse from dodgy managers - for example, I had a friend who worked at a supermarket that rostered him on for 3.75 hours, then 30 minutes later, rostered him on for another 3.75 hours. This 'split shift' meant that they didn't have to give him the mandatory paid 30 minute lunch break for an 8-hour shift.
Same goes for it being extremely busy and calling someone who is off and asking if they wanted to come in to make some extra money.
This sounds like a balance, but it really isn't. "Would you agree to do more work" is not the opposite of "I'm reneging on our agreement for your current work" - the latter is unilateral.
Hospitality sucks. When I was in my early 20s, more than half the people I knew worked in hospitality. Now I'm 40, only one still remains in hospitality. It's an abusive industry that people get out of if they can - in general, it's short hours, odd shifts, bad pay, crap managers with little or no training, and no job security. Screw defending the practices of that industry.