The "difference" starts with whether the Mexican truck is even insured.
This afternoon, National Public Radio had a long piece about hit-and-run wrecks being the norm in Mexico - in large part because driving uninsured is so much the norm down there; Mexican police say it's even common for buses down there to do hit-and-runs (think about that the next time you see one of those "Mexican bus" operations in your town!) - and they, too, are often uninsured.
Still want "Juan" driving an 18-wheeler with Mexican plates in the next lane?
IMMIGRATION resource library - with public-health facts of immigration!
All drivers have to show proof of insurance to cross the border in either direction. I have driven across many borders on four continents and always had to show proof of insurance. There are international insurance companies that issue special policies.
Next false issue?