Ya.. may be in future we will not have to use these prefixes for different browser but now every browser have there different css libraries so as a front end developer We have to use these prefixes in our css other wise some browsers will not render our css. This is how they work and we have follow them.
Here is the liks of Webkit and Firefox prefix libraries
http://developer.apple.com/library/safari/#documentation/InternetWeb/Conceptual/SafariVisualEffectsProgGuide/Gradients/Gradient.html
https://developer.mozilla.org/en-US/docs/CSS/CSS_Reference/Mozilla_Extensions
