Speaking from personal experience, I think the positives of this outweigh the negatives. I've had many customer-interactive part-time jobs in my life, and I think that it can be great fun when adults have their children do the interacting. So long as the store is not too busy, and the parents provide intervention when it is necessary (as in this particular story), I think that most people will not be inconvenienced significantly.
More importantly, I think that forcing your kids to do these types of interactions from a young age is very instrumental in their growth and development. While I am not well-versed in childhood development, I think that I rarely (if ever) was encouraged to do these sorts of things on my own when I was young, and that (possibly due in part to this) I had to break an irrational phobia of these types of social interactions at around the age of 18.
I was literally afraid to ask for help in a store, or to call a business for almost any reason. Mentally preparing for phone calls with strangers, even something as innocuous as finding out store hours, could leave me shaking.
Fortunately, I've managed to overcome this anxiety. I can't know for certain whether more of these types of interaction at a young age would have prevented this problem, but I think that it is reasonable to believe that it could have. The slight inconvenience is a small price to pay for this sort of developmental skill-building.
That's not to say that some people don't need to reign in their kids now and then, just that an appropriate amount of interaction is healthy and really not very annoying at all to others.