I have some past experience working in the courts in my state, and I know there are many judges who are perfectly fine with dismissing minor traffic infractions for no reason other than that they feel like it. If you've got an otherwise clean traffic abstract and sent in a reasonable sounding letter contesting the infraction, these judges probably aren't going to thoroughly read through every word of it and contrast it with what was alleged in the citation. They don't really care about the city making an extra $173 off your parking ticket -- they just want to get through their citation reviews before lunch. Case dismissed.
So I am not surprised at all by the success of DoNotPay for minor traffic infractions. Most traffic courts are heavily strained by heavy case loads. If you give them a reason to throw your case out so they can go home on time, by all means, they will take it.