Another gem from the decision (EDIT: as @DavePhD correctly points out, this quote is from the earlier decision on the motion to suppress, but the S.Ct. decision supports this view more or less fully in paragraph 43, added below):
There is no evidence that Deputy Small "commanded" Mr. Vogt to roll down his window by tapping on the window and motioning that he roll down his window.
 Vogt's assertion that he was seized because of Deputy Small's "command" to roll down the window also is unpersuasive. The circuit court found in its decision on the motion to suppress that "[t]here is no evidence that Deputy Small 'commanded' Mr. Vogt to roll down his window by tapping on the window and motioning that he roll down his window." At trial, the court found that Deputy Small's testimony "would indicate that he wasn't commanding [Vogt] to do anything, . . . that he was simply trying to make contact." Even though the circuit court noted that Deputy Small maybe "wasn't quite as subtle as he thought he was being," the court still determined that Deputy Small's conduct was not so intimidating as to constitute a seizure. Thus, Vogt's arguments that he was seized due to a "command" from Deputy Small are unavailing.
On the flip side, of course, if you just try to leave in response to such an action by an officer, this will likely be found to constitute resisting arrest. In such a case, I expect the court would have the epiphany that there is no other reasonable way for an officer to make a show of authority to a suspect in a car whose windows are closed. Indeed, this seems to have bothered the circuit court:
The officer also testified that he did not block the vehicle in, that the vehicle could have gotten around him. So there are a few factual distinctions as far as the testimony. It's not a very bright line, and I don't know how a driver knows the difference between a command and a suggestion, particularly when we're talking about a physical movement, the knocking on the window.
Of course, you wouldn't want to fail to obey a command, because that can qualify as resisting arrest. Wikipedia has this to state about the crime of resisting arrest:
The courts in the United States of America regard resisting arrest as a separate charge or crime in addition to other alleged crimes committed by the arrested person. It is possible to be charged, tried and convicted on this charge alone, without any underlying cause for the original decision to arrest.
Bottom line, it's a Catch-22 that ensures that there is not much you can do when your car reeks of booze and a cop taps on the window and motions that you roll down your window. If you roll down the window, the officer just suggested that you do so and you're set for a DUI. If you try to drive off, it will turn out that the officer commanded that you roll down the window, and you're set for resisting arrest (which the cop can now legitimately arrest you for), plus DUI.
The idea that the officer would've simply let the defendant go about his business if he had simply driven off can be seen as an example of legal fiction.