Green card holders (permanent US residents) are NOT counted as internationals when schools report acceptances/enrollments to AMCAS.
RE: escrow account requirements–
AAMC and LCME requires all US med schools to report their drop-out rates. LCME uses the drop out rate as a factor in accreditation. If the drop out rate gets too high (think >5%) for any reason, the school is placed on probation–which is something all med schools want to avoid like the plague.
I think most of the increase in the number of international applications/international matriculants you’re seeing is due to Canadian applicants. Admission to med school in Canada is extremely difficult (think California on steroids) and getting a residency slot in Canada as a IMG is also extremely difficult (tougher than in the US) so more Canadians are applying to US schools. Because both US and Canadian med schools are accredited by the same organization, Canadian grads of US med schools are not considered IMGs in Canada. (Also the Canadian government provides special loans for Canadian citizens attending med school in the US.)