Most likely culprit for airspace violations in the US:
GPS in statue miles, rest of the World in nautical.
Don't know how common that would be elsewhere.
Also, someone mentioned an a/c at FL360 depicting 6 miles from the site. In the US, our sites overlap enough that a mosaic (composite) picture is formed and displayed on the scope. At altitude, over a long range radar site, you would not be picked up by that site, instead, your transponder would be received by the other sites that overlap. Position is then accurately interpolated by the machine.
Do other countries not use mosaic radar for their area control?