As I say, I am aware of the technical difference. The separate student, work, etc, visa's are routinely used as a means of legally immigrating to the US. Once here a large percentage begin to seek out more permanent status, often letting their current status expire.
No matter though, they know there is little chance of being caught because the system is undermanned and out of control. Which brings us back to the original point.
Seriously, it would be far more humanitarian to make these people stay in their home countries agitating for representitive governments there. It won't be cleaned up otherwise no matter how many fake treaties are enacted. If the partner countries aren't held to corrective measures their peasants will continue seeking to come here. Demand they FIX IT, don't help perpetuate those country's legacy of corruption.