That's kind of hard to believe if these are the type of cameras that take a perfectly clear photo of the driver behind the wheel along with laser or radar speed measurement. I mean, you can show up in traffic court in Washington requesting a mitigation of the fine, but what kind of a contested defense would one muster to the violation? (other than the usual calibration issues, but the WSP has been extremely fastidious about procedures recently). It is true that the prosecutor's office (usually the county-District Court here) has to devote staff time to filling requests for discovery.
I can think of a few things, all involving cameras. A branch over the speed limit sign the most odvious...leaves deflecting the radar beam...some other reason it points in the wrong direction...All bs and some of it contrived, but still it requires resources to prove against and what's to lose? A little time? I'ld give it up along with a slightly higher fine just to be a pain.