I think the problem, though, is when did you start looking at them? If the world started on that day, then fine, but the reality is that the day you started looking at them was not their first day in operation. Who took the first shot doesn't really matter, because that first shot, no matter who made it, would (in the context of what you're saying) seem pretty trivial. The point is that we've moved together (DMV workers and folks going to the DMV for service) down this path. The lack-of-smile you're referring to is almost surely a reflection of how the last ten people treated that DMV worker.
And that's almost surely a reflection of how nasty people generally are to service workers who refuse to give them what they want, regardless of whether the policies and procedures and laws governing the provision of that service are actually "at fault" with regard to the denial. People generally want what they want and many have little or no capacity to gracefully accept that the person providing them service is just doing their job well.
Expecting that a human being would not show the scars from the disrespect bestowed on them from the last ten people that they served is unreasonable. Sure, a few remarkable people have the ability to slough off such abuse, and treat every person asking for service individually. However, such gems are highly desired by premium-grade service providers in the private sector: Taxpayers are, generally, cheap, and won't brook with government paying premium salaries for premium quality service workers. Similarly, you're not going to find mainstream service providers paying top-dollar for superior service workers, because mainstream customers aren't going to brook with paying a premium for such service. Mainstream customers are much more focused on getting the lowest price.