Put yourself in the place of the latecomers. When have you gotten more than you had earned? What was your reaction? Why was Jesus silent on their reaction?
Put yourself in the place of the landowner. How should you pay your workers? Who has worked for you? Did you always reward them according to what they deserved to get? Have you ever been generous beyond what equity would call for? If so, were you confronted with more unhappy or more happy recipients?
Robert Frost's poem Death of the Hired Man (http://www.poets.org/viewmedia.php/prmMID/19369) suggests that some of us are able to recognize a need to care for someone who may not have earned that care.
In Jesus' time many laborers had been thrown out of work as a result of the economic conditions (Allen & Williamson, Preaching the Gospel).
In our time, we still have to figure out how to deal with laborers who have arrived later. Here's one way that we are trying, Group Helps Those in Raid http://www.thedenverchannel.com/politics/11056487/detail.html
You might also want to read: Undocumented workers
For an update, see http://www.commondreams.org/view/2011/04/11-9