I've been telling the IE team to do this since IE 9. In reality, the purpose of vendor prefixes is to keep two vendors from using the same name for two distinctly different behaviors. The current prefix model does that.

After a prefixed extension gains market adoption, it serves to indicate which implementation is authoritative. -webkit means you better do it the way webkit does it.

Any browser that won't make use of the author's intent, when that intent is unambiguous and easy to determine, is just shooting itself in the foot.