Honestly, it can be a little intimidating to new customers--in the way Starbucks orders are intimidating at first. It also can be annoying because the greetings ring loudly every time someone enters, so if you are dining, you can still hear it.
The goodness of the greeting far outweighs the negatives.
At least at Gates, customers know they are welcome. They know the employees are eager to take their order and prepare their meals. How often do you feel the opposite?
How often do you wonder if the employees are actually told to leave their brains at home and simply follow a procedure manual upon arrival at work? Many seem to have the attitude, "I'd love this job if it weren't for the customers!"
I'd rather hear, "Hi, may I help you?" a million times than feel like I'm annoying just by showing up.
When companies take care of their customers, we're likely to return. Thus, taking care of one stakeholder, the customer, benefits all stakeholders. Employees have jobs, suppliers get business, investors get a return, and local communities get a thriving contributor (hopefully).
The BBQ joint is doing something right alright: they are eager to please their customers with service, and their food is great too.