Post 3 is not right about the slaves being treated the same in the Caribbean. This is just an incorrect statement. Slaves were treated much more brutally there. Harsher conditions led to slave populations there being unable to sustain themselves naturally. Slaves on the mainland had enough children and died late enough for their population to grow "naturally" -- without more slaves being imported.
One interesting point is that the first recorded Africans to be bought on the Mainland U.S. were not true slaves as later defined by law and custom. Instead, they were assigned status as indentured servants, and some of them were able to work off their debt and become free. There were actually African slave-holders living in Virginia. Now, this is not to say that the distinction might be more of a semantic one -- servants or slaves, their treatment was still brutal. However, the institutionalization of slavery took hold in stages, rather than all at once.
In general, slaves were treated about the same in America and the Caribbean. It always seemed to me that there were larger plantations in the Caribbean, and therefore more slaves. The biggest difference is that in some Caribbean islands, such as Haiti, the slaves revolted and took over the country.
The primary difference between the slave trade in the American Colonies (and, later, the U. S.) and the Caribbean is that slaves were used primarily for the harvest and production of sugar cane in the West Indies. Tobacco production was the main use for American slaves, particularly in the South. Death rates were much higher n the Caribbean, often exceeding birth rates.