What part of immigration to the US do you not understand?

http://reason.com/blog/2008/09/24/new-at-reason-mike-flynn-shikh
I saw this posted on one of my Blogmate's page. While I knew that it is easier to come to the US if you have a Master's degree and employed here, I didnt have a clue about how difficult it is for someone with no education or skill to get here. This gave me an understanding about why there is illegal immigration across the border from Mexico or other nations where making a living is not guaranteed.