Here's some more info on the tail wind. It really a matter of certification process for transport aircraft. They are only tested to a maximum component, most of the time this is 10 kts. Traffic has a lot to do with it also. You can get a landing against the flow if traffic is light or late at night and get straight in landing with a light tail wind provided as Drcoopster states there is enough runway. Depending on which type of operations you are conducting (Part 121, Part 135, Part 91) there is a whole slue of regulations, guideline and procedure both company and FAA/CAA imposed that must be followed. Most of which deal with safety.
Here's an interesting look at just how many airplanes are in the sky at a given time. So lots of time you just have to go with the flow.