The US has always set different immigration policies for specific countries that we consider to have oppressive governments, or who we have other political interests with. For example, we let in entire boatloads of Vietnamese immigrants, without making any of them swim and without adjusting immigration quotas for other countries.
It's hard to draw a parallel between our national policy concerning Cuba with our national policy concerning Mexico. Yes, the quality of life in Cuba is arguably better than the quality of life in parts of Mexico, but the whole political prisoner and nation isolation bit we have going on with Cuba makes our policy on Cuban immigration a special case.
It's not quite apples and oranges... more like comparing tangerines and oranges. They are similar issues, but it's definately not the same situation.